Introduce new TLS error codes

Introduce new codes:
* MBEDTLS_ERR_SSL_UNSUPPORTED_EXTENSION
* MBEDTLS_ERR_SSL_NO_APPLICATION_PROTOCOL

These are returned when the corresponding alert is raised.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index c41eff2..7e94102 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -749,7 +749,7 @@
     /* If we get there, no match was found */
     mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
                             MBEDTLS_SSL_ALERT_MSG_NO_APPLICATION_PROTOCOL );
-    return( MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE );
+    return( MBEDTLS_ERR_SSL_NO_APPLICATION_PROTOCOL );
 }
 #endif /* MBEDTLS_SSL_ALPN */