Further adapt prototypes of ticket functions

Moving everything in ticket_keys structure, that will soon become
ticket_context.
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 9651014..3f3a369 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -760,6 +760,7 @@
     mbedtls_aes_context enc;                /*!< encryption context                  */
     mbedtls_aes_context dec;                /*!< decryption context                  */
     unsigned char mac_key[16];      /*!< authentication key                  */
+    uint32_t ticket_lifetime;
 };
 #endif /* MBEDTLS_SSL_SESSION_TICKETS */
 
@@ -896,10 +897,6 @@
     unsigned int badmac_limit;      /*!< limit of records with a bad MAC    */
 #endif
 
-#if defined(MBEDTLS_SSL_SESSION_TICKETS)
-    int ticket_lifetime;            /*!< session ticket lifetime (seconds)  */
-#endif
-
     unsigned char max_major_ver;    /*!< max. major version used            */
     unsigned char max_minor_ver;    /*!< max. minor version used            */
     unsigned char min_major_ver;    /*!< min. major version used            */