websocket: don't return transport.ErrListenerClosed on closing listener

[sukunrt]

closes #2865

ErrListenerClosed is supposed to be returned by Accept when listener is closed.

[ineiti]

LGTM - That's more than I could do :)

Is the <- l.closed also fulfilled if the closing fails and returns an error?

[sukunrt]

@ineiti Yes, l.closed chan should always be closed provided you started listening on an address. This is always true if you're calling any of the public methods on the transport.