Fix sparse warnings: non-ANSI function declarations, 0 used as pointer
diff --git a/extensions/libxt_mac.c b/extensions/libxt_mac.c
index a9874cd..69fbc56 100644
--- a/extensions/libxt_mac.c
+++ b/extensions/libxt_mac.c
@@ -24,8 +24,8 @@
 }
 
 static const struct option opts[] = {
-	{ "mac-source", 1, 0, '1' },
-	{0}
+	{ "mac-source", 1, NULL, '1' },
+	{ }
 };
 
 static void