Turn comments of 1.3 record transforms into Doxygen documentation

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 34353da..960a262 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1342,8 +1342,8 @@
                                                                   *    it references.                  */
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
-    /* The application data transform in TLS 1.3.
-     * This pointer owns the transform it references. */
+    /*! The application data transform in TLS 1.3.
+     *  This pointer owns the transform it references. */
     mbedtls_ssl_transform *MBEDTLS_PRIVATE(transform_application);
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */