ssl_ticket.c: Fix ticket lifetime enforcement

Take into account that the lifetime of
tickets can be changed through the
mbedtls_ssl_ticket_rotate() API.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index 6d59c12..5842049 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -50,6 +50,10 @@
 #if defined(MBEDTLS_HAVE_TIME)
     mbedtls_time_t MBEDTLS_PRIVATE(generation_time); /*!< key generation timestamp (seconds) */
 #endif
+    /*! Lifetime of the key in seconds. This is also the lifetime of the
+     *  tickets created under that key.
+     */
+    uint32_t MBEDTLS_PRIVATE(lifetime);
 #if !defined(MBEDTLS_USE_PSA_CRYPTO)
     mbedtls_cipher_context_t MBEDTLS_PRIVATE(ctx);   /*!< context for auth enc/decryption    */
 #else