Replace `start` with `ticket_creation`

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_ticket.c b/library/ssl_ticket.c
index c89a5cd..05249ea 100644
--- a/library/ssl_ticket.c
+++ b/library/ssl_ticket.c
@@ -498,16 +498,17 @@
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
     if (session->tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
         /* Check for expiration */
-        mbedtls_ms_time_t ticket_age = mbedtls_ms_time() - session->start;
+        mbedtls_ms_time_t ticket_age = mbedtls_ms_time() - session->ticket_creation;
         mbedtls_ms_time_t ticket_lifetime = ctx->ticket_lifetime * 1000;
 
         if (ticket_age < 0 || ticket_age > ticket_lifetime) {
             ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
             goto cleanup;
         }
-    } else
+    }
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
-    {
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+    if (session->tls_version == MBEDTLS_SSL_VERSION_TLS1_2) {
         /* Check for expiration */
         mbedtls_time_t current_time = mbedtls_time(NULL);
 
@@ -517,6 +518,7 @@
             goto cleanup;
         }
     }
+#endif
 #endif /* MBEDTLS_HAVE_TIME */
 
 cleanup:
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f855576..d727636 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2537,7 +2537,7 @@
 
 #if defined(MBEDTLS_HAVE_TIME) && defined(MBEDTLS_SSL_SRV_C)
     if (session->endpoint == MBEDTLS_SSL_IS_SERVER) {
-        MBEDTLS_PUT_UINT64_BE((uint64_t) session->start, p, 0);
+        MBEDTLS_PUT_UINT64_BE((uint64_t) session->ticket_creation, p, 0);
         p += 8;
     }
 #endif /* MBEDTLS_HAVE_TIME */
@@ -2616,7 +2616,7 @@
         if (end - p < 8) {
             return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
         }
-        session->start = MBEDTLS_GET_UINT64_BE(p, 0);
+        session->ticket_creation = MBEDTLS_GET_UINT64_BE(p, 0);
         p += 8;
     }
 #endif /* MBEDTLS_HAVE_TIME */
diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 7b8cc6e..744e984 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -193,15 +193,15 @@
 #if defined(MBEDTLS_HAVE_TIME)
     now = mbedtls_ms_time();
 
-    if (now < session->start) {
+    if (now < session->ticket_creation) {
         MBEDTLS_SSL_DEBUG_MSG(
             3, ("Invalid ticket start time ( now = %" MBEDTLS_PRINTF_MS_TIME
                 ", start = %" MBEDTLS_PRINTF_MS_TIME " )",
-                now, session->start));
+                now, session->ticket_creation));
         goto exit;
     }
 
-    server_age = now - session->start;
+    server_age = now - session->ticket_creation;
 
     /* RFC 8446 section 4.6.1
      *
@@ -2880,7 +2880,7 @@
     MBEDTLS_SSL_DEBUG_MSG(2, ("=> prepare NewSessionTicket msg"));
 
 #if defined(MBEDTLS_HAVE_TIME)
-    session->start = mbedtls_ms_time();
+    session->ticket_creation = mbedtls_ms_time();
 #endif
 
     /* Set ticket_flags depends on the advertised psk key exchange mode */