1. now when the autopilot start, the ap_mode is set to be AP_MODE_NAV
2. the RC functionality is disabled (maybe)
3. the datalink should be able to change the ap_mode

TODO: add message to parsed
1. add pprz_get_quad_swarm_report() on the GCS side to read the report from
quadcopter.
2. add pprz_get_quad_swarm_ack() on the GCS side to read the ack from quadcopter
3. add pprz_set_quad_swarm_ack() on the GCS side to generate pprz quad_swarm_ack_forwarded message to quadcopter
4. add handler of quad_swarm_ack in quad_swarm.h

Now the GCS can sucessfully read GPS coordinate sent by the quadcopter

TODO:
->write how to choose reference point
->write start engine
->test message from multiple quadcopter