fix pkgs used for netcat when qemu-vm.nix does guestfwd (#512272)

            + "${guest.address}:${toString guest.port},"

          else

            "'guestfwd=${proto}:${guest.address}:${toString guest.port}-"

            + "cmd:${pkgs.netcat}/bin/nc ${host.address} ${toString host.port}',"

            + "cmd:${hostPkgs.netcat}/bin/nc ${host.address} ${toString host.port}',"

        );

        restrictNetworkOption = lib.optionalString cfg.restrictNetwork "restrict=on,";

      in