fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_limit.c b/extensions/libxt_limit.c
index 92cecf4..65a8df3 100644
--- a/extensions/libxt_limit.c
+++ b/extensions/libxt_limit.c
@@ -32,7 +32,7 @@
 static const struct option limit_opts[] = {
 	{ "limit", 1, NULL, '%' },
 	{ "limit-burst", 1, NULL, '$' },
-	{ }
+	{ .name = NULL }
 };
 
 static