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_misc.h b/library/ssl_misc.h
index 2621d20..7e060d3 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -625,7 +625,7 @@
     uint8_t tls13_kex_modes; /*!< Key exchange modes supported by the client */
 #endif
 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
-    int tls13_session_tickets;         /*!< number of session tickets */
+    int new_session_tickets_count;         /*!< number of session tickets */
 #endif
 #endif /* MBEDTLS_SSL_SRV_C */