read from the client-side socket

This fixes a bug whereby the accept loop invokes the read loop with the server-side socket rather than the *client-side* socket. Reads were being dropped on the floor.

Not sure how this happened and it was tricky to track down because the error didn't appear in the (main) JavaScript console :-/

Tested by hacking socks-rtc's TcpEchoServer into its Chrome extension and eyeballing the telnet output:
https://github.com/uProxy/socks-rtc/compare/yangoon-echo-server-test