Send a packet through the link interface.

        pk -- Packet to send
        expect_answer -- True if a packet from the Crazyflie is expected to
                         be sent back, otherwise false

def send_packet(self, pk, expected_reply=(), resend=False, timeout=0.2):
        """
        Send a packet through the link interface.

        pk -- Packet to send
        expect_answer -- True if a packet from the Crazyflie is expected to
                         be sent back, otherwise false

        """
        self._send_lock.acquire()
        if self.link is not None:
            if len(expected_reply) > 0 and not resend and \
                    self.link.needs_resending:
                pattern = (pk.header,) + expected_reply
                logger.debug(
                    'Sending packet and expecting the %s pattern back',
                    pattern)
                new_timer = Timer(timeout,
                                  lambda: self._no_answer_do_retry(pk,
                                                                   pattern))
                self._answer_patterns[pattern] = new_timer
                new_timer.start()
            elif resend:
                # Check if we have gotten an answer, if not try again
                pattern = expected_reply
                if pattern in self._answer_patterns:
                    logger.debug('We want to resend and the pattern is there')
                    if self._answer_patterns[pattern]:
                        new_timer = Timer(timeout,
                                          lambda:
                                          self._no_answer_do_retry(
                                              pk, pattern))
                        self._answer_patterns[pattern] = new_timer
                        new_timer.start()
                else:
                    logger.debug('Resend requested, but no pattern found: %s',
                                 self._answer_patterns)
            self.link.send_packet(pk)
            self.packet_sent.call(pk)
        self._send_lock.release()