nixos/rdnssd: define group; fix after #133166

nixos/modules/misc/ids.nix

@@ -220,7 +220,7 @@ in
       zope2 = 185;
       ripple-data-api = 186;
       mediatomb = 187;
-      rdnssd = 188;
+      #rdnssd = 188; #dynamically allocated as of 2021-09-18
       ihaskell = 189;
       i2p = 190;
       lambdabot = 191;

nixos/modules/services/networking/rdnssd.nix

@@ -72,8 +72,10 @@ in
 
     users.users.rdnssd = {
       description = "RDNSSD Daemon User";
-      uid = config.ids.uids.rdnssd;
+      isSystemUser = true;
+      group = "rdnssd";
     };
+    users.groups.rdnssd = {};
 
   };