gluon-config-mode-mesh-vpn: fix save() call for traffic limits

It doesn't seem like this mistake had any effect.

package/gluon-config-mode-mesh-vpn/files/lib/gluon/config-mode/wizard/0300-mesh-vpn.lua

@@ -56,7 +56,7 @@ function M.handle(data)
       uci:set("simple-tc", "mesh_vpn", "limit_egress", data._limit_egress:trim())
     end
 
-    uci:commit("simple-tc")
+    uci:save("simple-tc")
     uci:commit("simple-tc")
   end
 end