nixos/gammu-smsd: define group, fix after #133166

nixos/modules/misc/ids.nix

@@ -258,7 +258,7 @@ in
       rspamd = 225;
       # rmilter = 226; # unused, removed 2019-08-22
       cfdyndns = 227;
-      gammu-smsd = 228;
+      # gammu-smsd = 228; #dynamically allocated as of 2021-09-17
       pdnsd = 229;
       octoprint = 230;
       avahi-autoipd = 231;

nixos/modules/services/misc/gammu-smsd.nix

@@ -202,8 +202,8 @@ in {
   config = mkIf cfg.enable {
     users.users.${cfg.user} = {
       description = "gammu-smsd user";
-      uid = config.ids.uids.gammu-smsd;
-      extraGroups = [ "${cfg.device.group}" ];
+      isSystemUser = true;
+      group = cfg.device.group;
     };
 
     environment.systemPackages = with cfg.backend; [ gammuPackage ]