Pong not implemented

[jcheng5]

Section 5.5.2 of RFC 6455:

Upon receipt of a Ping frame, an endpoint MUST send a Pong frame in
response, unless it already received a Close frame.  It SHOULD
respond with Pong frame as soon as is practical.  Pong frames are
discussed in Section 5.5.3.

Looks to me like this needs to go at the end of the service function in websockets.R.