add support for vtol attitude offboard setpoints

[Boyang--Li]

The previous firmware dose not support off-board attitude control for VTOL vehicles.
We add support to this function in hover state by changing the mavlink message head.
We tested it with Gazebo simulation and indoor flight experiment, px4fmu-v2_lpe (log).

[dagar]

This looks okay, but I'm wondering if we should solve it slightly differently so that we don't need even more special handling if FW offboard is wanted later.

In VTOL the regular attitude controllers still subscribe to vehicle_attitude_setpoint, the virtual topics (mc_virtual_attitude_setpoint/fw_virtual_attitude_setpoint) are used by the vtol controller to intercept each position controller and facilitate transition.

If you instead blocked vehicle_attitude_setpoint publications in vtol_attitude (https://github.com/PX4/Firmware/blob/master/src/modules/vtol_att_control/vtol_att_control_main.cpp#L888) it would work for both MC and FW with no mavlink change. The only additional thing to consider is transition.

[dagar]

Here's the logic for publishing in the MC position controller. https://github.com/PX4/Firmware/blob/master/src/modules/mc_pos_control/mc_pos_control_main.cpp#L3180-L3200

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Closing as stale.