nixos-module/container/upstream: use internal core ipv4 address for port forwarding reflection

nix/nixos-module/container/upstream.nix

@@ -108,11 +108,7 @@ in
           else "${destination}:${toString sourcePort}";
         loopbackIPs =
           if reflect
-          then builtins.filter (ip: ip != null) (
-            map (net:
-              upstreamInterfaces.${net}.upstream.staticIpv4Address
-            ) (builtins.attrNames upstreamInterfaces)
-          )
+          then [ config.site.net.core.hosts4.${hostName} ]
           else [];
       }
     ) hostConf.forwardPorts;