Make nix scheduling options compatible with 21.11

modules/nix.nix

@@ -64,11 +64,15 @@ in
       keep-outputs = true
       keep-derivations = true
     '';
-
+  } // (if (builtins.compareVersions config.system.nixos.release "21.11" != -1) then {
     # Make nix build in background less noticeable
+    daemonCPUSchedPolicy = "batch";
+    daemonIOSchedPriority = 5; # 0-7
+  } else {
+    # TODO 21.11: remove
     daemonNiceLevel = 10;
     daemonIONiceLevel = 5; # 0-7
-  };
+  });
 
   nixpkgs.overlays = with inputs; [
     self.overlay