Source code checked in, #40796

Immediately exit Bind when the client socket has shut down. The SSH_MSG_CHANNEL_EOF message is now only sent from Close(bool), and we now only ever wait for an SSH_MSG_CHANNEL_CLOSE message once the client has shut down. The SSH_MSG_CHANNEL_EOF which is sent by the server is now only used to interrupt the blocking receive on the client socket, and close it.