nixos/geoclue2: make system service wait on network-online

In ee0b8a7eaa9 we made the user service wait on network-online, but
forgot about the system service. We need them _both_ to wait when the
wifi source is enabled.

nixos/modules/services/desktops/geoclue2.nix

···
     };
 
     systemd.services.geoclue = {
+      after = lib.optionals cfg.enableWifi [ "network-online.target" ];
       # restart geoclue service when the configuration changes
       restartTriggers = [
         config.environment.etc."geoclue/geoclue.conf".source