Rename identifiers containing double-underscore

Rename identifiers containing double-underscore (`__`) to avoid `__`.
The reason to avoid double-underscore is that all identifiers
containing double-underscore are reserved in C++. Rename all such
identifiers that appear in any public header, including ssl_internal.h
which is in principle private but in practice is installed with the
public headers.

This commit makes check-names.sh pass.

```
perl -i -pe 's/\bMBEDTLS_SSL__ECP_RESTARTABLE\b/MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED/g; s/\bMBEDTLS_KEY_EXCHANGE_(_\w+)_(_\w+)\b/MBEDTLS_KEY_EXCHANGE${1}${2}/g' include/mbedtls/*.h library/*.c programs/*/*.c scripts/data_files/rename-1.3-2.0.txt tests/suites/*.function
```
diff --git a/programs/ssl/mini_client.c b/programs/ssl/mini_client.c
index 4b8140e..b4346bb 100644
--- a/programs/ssl/mini_client.c
+++ b/programs/ssl/mini_client.c
@@ -88,7 +88,7 @@
 
 const char *pers = "mini_client";
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 const unsigned char psk[] = {
     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
     0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
@@ -211,7 +211,7 @@
 
     mbedtls_ssl_conf_rng( &conf, mbedtls_ctr_drbg_random, &ctr_drbg );
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
     mbedtls_ssl_conf_psk( &conf, psk, sizeof( psk ),
                 (const unsigned char *) psk_id, sizeof( psk_id ) - 1 );
 #endif
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index ab72f15..d6c3d77 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -201,7 +201,7 @@
 #define USAGE_CID ""
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #define USAGE_PSK_RAW                                               \
     "    psk=%%s              default: \"\" (disabled)\n"     \
     "                          The PSK values are in hex, without 0x.\n" \
@@ -223,7 +223,7 @@
 #define USAGE_PSK USAGE_PSK_RAW USAGE_PSK_SLOT
 #else
 #define USAGE_PSK ""
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 #if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
 #define USAGE_CA_CALLBACK                       \
@@ -1127,7 +1127,7 @@
 
     unsigned char buf[MAX_REQUEST_SIZE + 1];
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
     unsigned char psk[MBEDTLS_PSK_MAX_LEN];
     size_t psk_len = 0;
 #endif
@@ -1756,7 +1756,7 @@
     mbedtls_debug_set_threshold( opt.debug_level );
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
     /*
      * Unhexify the pre-shared key if any is given
      */
@@ -1775,7 +1775,7 @@
             goto exit;
         }
     }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     if( opt.psk_opaque != 0 )
@@ -2376,7 +2376,7 @@
     }
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     if( opt.psk_opaque != 0 )
     {
@@ -2414,7 +2414,7 @@
             goto exit;
         }
     }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
     if( opt.min_version != DFL_MIN_VERSION )
         mbedtls_ssl_conf_min_version( &conf, MBEDTLS_SSL_MAJOR_VERSION_3,
@@ -3314,7 +3314,7 @@
     mbedtls_free( context_buf );
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED) && \
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED) && \
     defined(MBEDTLS_USE_PSA_CRYPTO)
     if( opt.psk_opaque != 0 )
     {
@@ -3331,7 +3331,7 @@
                 ret = MBEDTLS_ERR_SSL_HW_ACCEL_FAILED;
         }
     }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED &&
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED &&
           MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index d23a700..4f66059 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -257,7 +257,7 @@
 #define USAGE_CID ""
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #define USAGE_PSK_RAW                                               \
     "    psk=%%s              default: \"\" (disabled)\n"     \
     "                          The PSK values are in hex, without 0x.\n" \
@@ -292,7 +292,7 @@
 #define USAGE_PSK USAGE_PSK_RAW USAGE_PSK_SLOT
 #else
 #define USAGE_PSK ""
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 #if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
 #define USAGE_CA_CALLBACK                       \
     "   ca_callback=%%d       default: 0 (disabled)\n"      \
@@ -1187,7 +1187,7 @@
 
 #endif /* SNI_OPTION */
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED) || \
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED) || \
     defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
 
 #define HEX2NUM( c )                        \
@@ -1233,7 +1233,7 @@
 
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 
 typedef struct _psk_entry psk_entry;
 
@@ -1345,7 +1345,7 @@
 
     return( -1 );
 }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 static mbedtls_net_context listen_fd, client_fd;
 
@@ -1748,7 +1748,7 @@
     int version_suites[4][2];
     io_ctx_t io_ctx;
     unsigned char* buf = 0;
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
     psa_algorithm_t alg = 0;
     psa_key_handle_t psk_slot = 0;
@@ -2626,7 +2626,7 @@
     }
 #endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
     /*
      * Unhexify the pre-shared key and parse the list if any given
      */
@@ -2644,7 +2644,7 @@
             goto exit;
         }
     }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
 #if defined(MBEDTLS_ECP_C)
     if( opt.curves != NULL )
@@ -3339,7 +3339,7 @@
     }
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
 
     if( strlen( opt.psk ) != 0 && strlen( opt.psk_identity ) != 0 )
     {
@@ -4232,7 +4232,7 @@
 #if defined(SNI_OPTION)
     sni_free( sni_info );
 #endif
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
     if( ( ret = psk_free( psk_info ) ) != 0 )
         mbedtls_printf( "Failed to list of opaque PSKs - error was %d\n", ret );
 #endif
@@ -4240,7 +4240,7 @@
     mbedtls_dhm_free( &dhm );
 #endif
 
-#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED) && \
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED) && \
     defined(MBEDTLS_USE_PSA_CRYPTO)
     if( opt.psk_opaque != 0 )
     {
@@ -4255,7 +4255,7 @@
                             (unsigned) psk_slot, (int) status );
         }
     }
-#endif /* MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED &&
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED &&
           MBEDTLS_USE_PSA_CRYPTO */
 
     mbedtls_ssl_free( &ssl );