fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_time.c b/extensions/libxt_time.c
index 29dd05d..c39ab1a 100644
--- a/extensions/libxt_time.c
+++ b/extensions/libxt_time.c
@@ -44,7 +44,7 @@
 	{"monthdays", true,  NULL, 'm'},
 	{"localtz",   false, NULL, 'l'},
 	{"utc",       false, NULL, 'u'},
-	{NULL},
+	{ .name = NULL }
 };
 
 static void time_help(void)