fix various issues

- get ticket_flags with function.
- improve output message and check it.
- improve `ssl_server2` help message

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 9f4926a..7a02c71 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1850,7 +1850,8 @@
             MBEDTLS_SSL_TLS1_3_TICKET_ALLOW_EARLY_DATA) == 0) {
         MBEDTLS_SSL_DEBUG_MSG(
             1,
-            ("EarlyData: rejected, denied by ticket permission bits."));
+            ("EarlyData: rejected, early_data not allowed in ticket "
+             "permission bits."));
         return;
     }
 
@@ -3222,10 +3223,11 @@
     unsigned char *p = buf;
     *out_len = 0;
 
-    if ((ssl->session->ticket_flags &
-         MBEDTLS_SSL_TLS1_3_TICKET_ALLOW_EARLY_DATA) == 0) {
+    if (mbedtls_ssl_session_get_ticket_flags(
+            ssl->session, MBEDTLS_SSL_TLS1_3_TICKET_ALLOW_EARLY_DATA) == 0) {
         MBEDTLS_SSL_DEBUG_MSG(
-            4, ("Skip early_data extension in NST for it is not allowed."));
+            4, ("early_data not allowed, skip early_data extension in "
+                "NewSessionTicket"));
         return 0;
     }