fix gcc warnings

Max Kellermann <max@duempel.org>
diff --git a/extensions/libxt_physdev.c b/extensions/libxt_physdev.c
index 144fbb4..e971d1e 100644
--- a/extensions/libxt_physdev.c
+++ b/extensions/libxt_physdev.c
@@ -30,7 +30,7 @@
 	{ "physdev-is-in", 0, NULL, '3' },
 	{ "physdev-is-out", 0, NULL, '4' },
 	{ "physdev-is-bridged", 0, NULL, '5' },
-	{ }
+	{ .name = NULL }
 };
 
 static int