Web Socket forwarder forwards close codes that are not valid on the wire

[jd3nn1s]

When faced with a Web Socket client that closes its TCP connection gracefully, but does not send a Web Socket close frame, gorilla/websocket correctly reports this as websocket close code 1006.

Oxy forwards code 1006 to the target Web Socket server. This is in breach of the Web Socket RFC6455 that states:

      1006 is a reserved value and MUST NOT be set as a status code in a
      Close control frame by an endpoint.  It is designated for use in
      applications expecting a status code to indicate that the
      connection was closed abnormally, e.g., without sending or
      receiving a Close control frame.

This can (and in the case of Jetty/Atmosphere does) lead to unexpected behavior on the server.