Called when first packet arrives from Crazyflie.

        This is used to determine if we are connected to something that is
        answering.

def _check_for_initial_packet_cb(self, data):
        """
        Called when first packet arrives from Crazyflie.

        This is used to determine if we are connected to something that is
        answering.
        """
        self.state = State.CONNECTED
        self.link_established.call(self.link_uri)
        self.packet_received.remove_callback(self._check_for_initial_packet_cb)