Connection to peer handler.

        We send bgp open message to peer and initialize related attributes.

def connection_made(self):
        """Connection to peer handler.

        We send bgp open message to peer and initialize related attributes.
        """
        assert self.state == BGP_FSM_CONNECT
        # We have a connection with peer we send open message.
        open_msg = self._peer.create_open_msg()
        self._holdtime = open_msg.hold_time
        self.state = BGP_FSM_OPEN_SENT
        if not self.is_reactive:
            self._peer.state.bgp_state = self.state
        self.sent_open_msg = open_msg
        self.send(open_msg)
        self._peer.connection_made()