Include configuration file to headers

Add inclusion to configration file in header files,
instead of relying on other header files to include
the configuration file. This issue resolves #1371
diff --git a/include/mbedtls/ssl_ticket.h b/include/mbedtls/ssl_ticket.h
index b2686df..a84e781 100644
--- a/include/mbedtls/ssl_ticket.h
+++ b/include/mbedtls/ssl_ticket.h
@@ -24,6 +24,12 @@
 #ifndef MBEDTLS_SSL_TICKET_H
 #define MBEDTLS_SSL_TICKET_H
 
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
 /*
  * This implementation of the session ticket callbacks includes key
  * management, rotating the keys periodically in order to preserve forward