Separate accepting TLS 1.3 middlebox compatibility from sending it

The compile-time option MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE gates both
support for interoperability with a peer that uses middlebox compatibility
mode, and support for activating that mode ourselves. Change code that is
only needed for interoperability to be guarded by
MBEDTLS_SSL_TLS1_3_ACCEPT_COMPATIBILITY_MODE.

As of this commit, MBEDTLS_SSL_TLS1_3_ACCEPT_COMPATIBILITY_MODE is always
enabled: there is no way to disable it, and there are no tests with it
disabled.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 2bdad84..86463bc 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -5066,7 +5066,7 @@
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
         if (ssl->tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
-#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
+#if defined(MBEDTLS_SSL_TLS1_3_ACCEPT_COMPATIBILITY_MODE)
             MBEDTLS_SSL_DEBUG_MSG(1,
                                   ("Ignore ChangeCipherSpec in TLS 1.3 compatibility mode"));
             return MBEDTLS_ERR_SSL_CONTINUE_PROCESSING;
@@ -5074,7 +5074,7 @@
             MBEDTLS_SSL_DEBUG_MSG(1,
                                   ("ChangeCipherSpec invalid in TLS 1.3 without compatibility mode"));
             return MBEDTLS_ERR_SSL_INVALID_RECORD;
-#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */
+#endif /* MBEDTLS_SSL_TLS1_3_ACCEPT_COMPATIBILITY_MODE */
         }
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
     }