fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_sctp.c b/extensions/libxt_sctp.c
index de8948c..4b9166a 100644
--- a/extensions/libxt_sctp.c
+++ b/extensions/libxt_sctp.c
@@ -73,7 +73,7 @@
 	{ .name = "destination-port", .has_arg = 1, .val = '2' },
 	{ .name = "dport", .has_arg = 1, .val = '2' },
 	{ .name = "chunk-types", .has_arg = 1, .val = '3' },
-	{ }
+	{ .name = NULL }
 };
 
 static void