babeld module: updated example config

Previosuly the example config did feature the deprecated `wired`
paramter. Wired can now be configured using the `type` parameter.

nixos/modules/services/networking/babeld.nix

···
         type = types.nullOr (types.attrsOf types.unspecified);
         example =
           {
-            wired = true;
+            type = "tunnel";
             "split-horizon" = true;
           };
       };
···
         type = types.attrsOf (types.attrsOf types.unspecified);
         example =
           { enp0s2 =
-            { wired = true;
+            { type = "wired";
               "hello-interval" = 5;
               "split-horizon" = "auto";
             };