bird service: add bird to systemPackages

For the tool birdc to monitor and configure bird.

Changed files
+1
nixos
modules
services
networking
+1
nixos/modules/services/networking/bird.nix
···
###### implementation
config = mkIf cfg.enable {
systemd.services.${variant} = {
description = "BIRD Internet Routing Daemon";
wantedBy = [ "multi-user.target" ];
···
###### implementation
config = mkIf cfg.enable {
+
environment.systemPackages = [ pkg ];
systemd.services.${variant} = {
description = "BIRD Internet Routing Daemon";
wantedBy = [ "multi-user.target" ];