mavsys: mode: add solutions for setting AUTO.MISSION and AUTO.LOITER modes

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Also the enums are updated - can push this to another PR if needed.

[khancyr]

looks like rebase error ^^

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That's fixed @khancyr. thanks

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Looks like we don't need to unset the datalink failsafe. For PX4, the heartbeat type published by sys_status, for now, needs to be of type MAV_TYPE_GCS so to be accepted and published on the telemetry_status uORB msg and that way set the datalink stream. IOT it be accepted also with MAV_TYPE_ONBOARD_CONTROLLER, I will purpose a patch to the Firmware.
And that is not all: https://github.com/PX4/Firmware/blob/master/src/modules/mavlink/mavlink_receiver.cpp#L1718 - the 1st condition is that msg->sysid != mavlink_system.sysid, so we cannot have system_id == tgt_system_id. And that's why I'm adding that option by default to the launch files.

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@shakthi-prashanth-m for your interest.

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@khancyr in Ardupilot is there any special case like this? Do you treat the hearbeat differently according to the MAV_TYPE?

[vooon]

Mavros sysid may be set via url, addition to launch is not required.
But for me that check looks weird, because OBC is part of same Unmanned System as FCU.

So FCU should understand when (hb.sysid == my.sysid && hb.type == OBC) - we have link with our OBC.

[TSC21]

It can't. If the sysid is the same, it will start listening to its own hb. What may make sense is to make a check to the component id