fix various issues

- Improve comments
- Align count variable name to `new_session_tickets_count`
- move tickets_count init to handshake init

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 7807408..40ac476 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -2617,10 +2617,23 @@
 static int ssl_tls13_write_new_session_ticket_coordinate( mbedtls_ssl_context *ssl )
 {
     /* Check whether the use of session tickets is enabled */
-    if( ssl->conf->f_ticket_write == NULL ||
-        ssl->handshake->tls13_session_tickets == 0 )
+    if( ssl->conf->f_ticket_write == NULL )
     {
-        MBEDTLS_SSL_DEBUG_MSG( 2, ( "new session ticket is not enabled" ) );
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "NewSessionTicket: disabled,"
+                                        " callback is not set" ) );
+        return( SSL_NEW_SESSION_TICKET_SKIP );
+    }
+    if( ssl->conf->new_session_tickets_count == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "NewSessionTicket: disabled,"
+                                        " configured count is zero" ) );
+        return( SSL_NEW_SESSION_TICKET_SKIP );
+    }
+
+    if( ssl->handshake->new_session_tickets_count == 0 )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 2, ( "NewSessionTicket: all tickets have "
+                                        "been sent." ) );
         return( SSL_NEW_SESSION_TICKET_SKIP );
     }
 
@@ -2642,9 +2655,9 @@
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> prepare NewSessionTicket msg" ) );
 
     if( ssl->handshake->resume == 1 )
-        ssl->handshake->tls13_session_tickets = 0;
+        ssl->handshake->new_session_tickets_count = 0;
     else
-        ssl->handshake->tls13_session_tickets--;
+        ssl->handshake->new_session_tickets_count--;
 #if defined(MBEDTLS_HAVE_TIME)
     session->start = mbedtls_time( NULL );
 #endif
@@ -2890,12 +2903,6 @@
         /* start state */
         case MBEDTLS_SSL_HELLO_REQUEST:
             mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_CLIENT_HELLO );
-#if defined(MBEDTLS_SSL_PROTO_TLS1_3) && defined(MBEDTLS_SSL_SESSION_TICKETS)
-            ssl->handshake->tls13_session_tickets =
-                ssl->conf->new_session_tickets ?
-                    ssl->conf->new_session_tickets :
-                    MBEDTLS_SSL_TLS1_3_DEFAULT_NEW_SESSION_TICKETS;
-#endif
             ret = 0;
             break;
 
@@ -3014,7 +3021,7 @@
              */
             ret = 0;
 
-            if( ssl->handshake->tls13_session_tickets == 0 )
+            if( ssl->handshake->new_session_tickets_count == 0 )
                 mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_HANDSHAKE_OVER );
             else
                 mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_NEW_SESSION_TICKET );