Do not add a new field in the SSL config

We cannot add a new field in SSL config in
an LTS. Use `session_tickets` field instead.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 65ad324..58063c7 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -5595,8 +5595,8 @@
         if (ssl_tls13_is_new_session_ticket(ssl)) {
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
             MBEDTLS_SSL_DEBUG_MSG(3, ("NewSessionTicket received"));
-            if (ssl->conf->new_session_tickets_enabled ==
-                MBEDTLS_SSL_ENABLE_NEW_SESSION_TICKETS_ENABLED) {
+            if (mbedtls_ssl_conf_is_new_session_tickets_enabled(ssl->conf) ==
+                MBEDTLS_SSL_NEW_SESSION_TICKETS_ENABLED) {
                 ssl->keep_current_message = 1;
 
                 mbedtls_ssl_handshake_set_state(ssl,