Fix Protocol::handleDisconnect() invocation

This pull request fixes handleDisconnect() invocations on server protocols by passing in the correct socket.

Given a protocol implementation would try to invoke methods on the socket inside `handleDisconnect()`, the following would happen:

```
Exception lang.Error (Fatal error: Call to a member function close() on a non-object in ...)
  at peer.server.Server::service() [line 216 of Server.class.php] Undefined offset: 200
  at <main>::__output((0xae)'', 9) [line 0 of StackTraceElement.class.php]
```