nixos-module/container/wireguard: set ipv4 default route

nix/nixos-module/container/wireguard.nix

@@ -1,3 +1,4 @@
+# wireguard upstreams (like njalla and flpk, not like vpn dialup. see vpn-gw)
 { hostName, config, lib, pkgs, ... }:
 
 let
@@ -82,8 +83,11 @@ in
 
     # IPv4 default route
     networkConfig.DefaultRouteOnDevice = true;
-    # IPv6 default route
     routes = [ {
+      # IPv4 default route
+      routeConfig.Destination = "0.0.0.0/0";
+    } {
+      # IPv6 default route
       routeConfig.Destination = "::/0";
     } ];