Starts a new RPC session with given connection.

def _start_rpc_session(self, sock):
        """Starts a new RPC session with given connection.
        """
        session_name = RpcSession.NAME_FMT % str(sock.getpeername())
        self._stop_child_activities(session_name)

        rpc_session = RpcSession(sock, self)
        self._spawn_activity(rpc_session)