Set correct extra data to receive all clients

At least according to the admin_network.txt.
Implementation is not working and work has been put to investigate why.

Note: Polling information about individual clients works. I can also confirm
      I am sending 0xffffffff as extra parameter as I know that working with
      floats can be a hell. Luckily js seems to be friendly in this case.

      So in short: I wonder if this is actually a bug in openttd or simply
      me overlooking something.