desktop: make nameservers work with resolvconf, switch to quad9

hosts/desktop.nix

@@ -34,7 +34,9 @@ in
 
   networking = {
     networkmanager.enable = true;
-    nameservers = [ "1.1.1.1" "1.0.0.1" ];
+    # networking.nameservers doesn't apply to resolvconf
+    # nameservers = [ "9.9.9.9" "1.1.1.1" ];
+    resolvconf.extraConfig = "name_servers=\"9.9.9.9 1.1.1.1\"";
   };
 
   xdg.portal.enable = true;