nixos/libvirtd: Use preferred version of iptables

Author: zhaofengli

nixos/modules/virtualisation/libvirtd.nix

@@ -410,7 +410,7 @@ in
       etc."qemu/bridge.conf".text = lib.concatMapStringsSep "\n" (e: "allow ${e}") cfg.allowedBridges;
       systemPackages = with pkgs; [
         libressl.nc
-        iptables
+        config.networking.firewall.package
         cfg.package
         cfg.qemu.package
       ];