http: Upgrade/CONNECT request should detach its socket earlier

With Upgrade or CONNECT request, http.ClientRequest emits 'close' event
after its socket is closed. However, after receiving a response, the socket
is not under management by the request.

http.ClientRequest should detach the socket before 'upgrade'/'connect'
event is emitted to pass the socket to a user. After that, it should
emit 'close' event immediately without waiting for closing of the socket.

Fixes #2510.