Rename resumption_key and the hardcode len

`resumption_key` is better name.

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 1a5cfca..e665ec1 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -335,6 +335,13 @@
 #define MBEDTLS_SSL_SRV_CIPHERSUITE_ORDER_CLIENT  1
 #define MBEDTLS_SSL_SRV_CIPHERSUITE_ORDER_SERVER  0
 
+#if defined(MBEDTLS_SSL_PROTO_TLS1_3) && defined(MBEDTLS_SSL_SESSION_TICKETS)
+#if defined(MBEDTLS_SHA384_C)
+#define MBEDTLS_SSL_TLS1_3_TICKET_RESUMPTION_KEY_LEN        48
+#elif defined(MBEDTLS_SHA256_C)
+#define MBEDTLS_SSL_TLS1_3_TICKET_RESUMPTION_KEY_LEN        32
+#endif /* MBEDTLS_SHA256_C  */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 && MBEDTLS_SSL_SESSION_TICKETS */
 /*
  * Default range for DTLS retransmission timer value, in milliseconds.
  * RFC 6347 4.2.4.1 says from 1 second to 60 seconds.
@@ -1175,13 +1182,8 @@
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3) && defined(MBEDTLS_SSL_SESSION_TICKETS)
     uint32_t MBEDTLS_PRIVATE(ticket_age_add);               /*!< Randomly generated value used to obscure the age of the ticket */
-    uint8_t MBEDTLS_PRIVATE(key_len);                       /*!< PSK key length */
-
-#if defined(MBEDTLS_SHA384_C)
-    unsigned char MBEDTLS_PRIVATE(key)[48];                 /*!< key (48 byte) */
-#elif defined(MBEDTLS_SHA256_C)
-    unsigned char MBEDTLS_PRIVATE(key)[32];                 /*!< key (32 byte) */
-#endif /* MBEDTLS_SHA256_C  */
+    uint8_t MBEDTLS_PRIVATE(resumption_key_len);            /*!< resumption_key length */
+    unsigned char MBEDTLS_PRIVATE(resumption_key)[MBEDTLS_SSL_TLS1_3_TICKET_RESUMPTION_KEY_LEN];
 
 #if defined(MBEDTLS_HAVE_TIME) && defined(MBEDTLS_SSL_CLI_C)
     mbedtls_time_t MBEDTLS_PRIVATE(ticket_received);        /*!< time ticket was received */
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 93f58e0..672cb0f 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -2055,7 +2055,7 @@
                     MBEDTLS_SSL_TLS1_3_LBL_WITH_LEN( resumption ),
                     ticket_nonce,
                     ticket_nonce_len,
-                    session->key,
+                    session->resumption_key,
                     hash_length );
 
     if( ret != 0 )
@@ -2066,11 +2066,11 @@
         return( ret );
     }
 
-    session->key_len = hash_length;
+    session->resumption_key_len = hash_length;
 
     MBEDTLS_SSL_DEBUG_BUF( 3, "Ticket-resumed PSK",
-                           session->key,
-                           session->key_len );
+                           session->resumption_key,
+                           session->resumption_key_len );
 
     return( 0 );
 }