tls13: set key exchange mode in ticket_flags on client/server

Set the ticket_flags when:
  - server: preparing NST (new session ticket) message
  - client: postprocessing NST message

Clear the ticket_flags when:
  - server: preparing NST message
  - client: parsing NST message

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 980c225..f951813 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -2604,6 +2604,13 @@
     session->start = mbedtls_time(NULL);
 #endif
 
+    /* Set ticket_flags depends on the advertised psk key exchange mode */
+    mbedtls_ssl_tls13_session_clear_ticket_flags(session,
+                                                 MBEDTLS_SSL_TLS1_3_TICKET_FLAGS_MASK);
+    mbedtls_ssl_tls13_session_set_ticket_flags(session,
+                                               ssl->handshake->tls13_kex_modes);
+    MBEDTLS_SSL_DEBUG_TICKET_FLAGS(4, session->ticket_flags);
+
     /* Generate ticket_age_add */
     if ((ret = ssl->conf->f_rng(ssl->conf->p_rng,
                                 (unsigned char *) &session->ticket_age_add,