fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_tcp.c b/extensions/libxt_tcp.c
index b1f12a4..3274f08 100644
--- a/extensions/libxt_tcp.c
+++ b/extensions/libxt_tcp.c
@@ -34,7 +34,7 @@
 	{ "syn", 0, NULL, '3' },
 	{ "tcp-flags", 1, NULL, '4' },
 	{ "tcp-option", 1, NULL, '5' },
-	{ }
+	{ .name = NULL }
 };
 
 static void