net: websocket: pass HTTP upgrade request context to user callback

Passing HTTP upgrade request context to the user callback allows the
user to decide whether to accept or reject the websocket connection
based on the HTTP headers in the request. The primary reason for this is
to enable authentication of the websocket connection (e.g. via cookies
or Authorization header).

Signed-off-by: Matt Rodgers <mrodgers@witekio.com>