Do not set GCS mode as default

[ThomasDebrunner]

Setting the GCS mode as default has hidden side-effects. Most notably that the connection is considered a valid datalink, and thus affects datalink failsafes in Autopilots.

When used on-board, this is an unwanted side-effect. While you can configure this, the default is set to the "less-safe" option, which could leave a careless user in the situation where datalink failsafes get disabled unintentionally.

[JonasVautherin]

I am probably a bit biased because I always saw MAVSDK primarily as an API for ground stations, which can also be used on the other side (be it a companion or an autopilot). To me it feels like whoever uses MAVSDK for something other than a ground station should know that in the MAVLink world, they should care about their sysid/compid (I don't think MAVLink gives us the luxury to be careless users 🙈). MAVSDK provides a way to set them, and it changes the type accordingly (you can say that you want to be an autopilot or a companion computer, for instance).

In any case, it feels weird to set the sysid/compid to values reserved for a ground station (which is the default), and at the same time to not set the type to "ground station" 🤔. I agree that the specs are not completely clear (some sysid/compids seem to be attributed to some types, which probably should never have been the case), but that is what we have.

On top of that, it is a breaking change for all the current users of MAVSDK as a ground station... Maybe that could go in MAVSDK v2?

@julianoes what do you think?

[julianoes]

I can see the drawbacks of having a default that causes surprises, and I would always try to err on the side of safety/caution.

However, I'm not convinced changing it to Custom as custom implies something is customized, and not default/standard. My plan was to overhaul the configuration and component type stuff to sync the two concepts and share the enums, etc. It seems like it would also be a good idea to make the selection required in the constructor, to avoid defaults that don't work. This would be a change we could do with v2.

[julianoes]

@ThomasDebrunner what about something like this?

Mavsdk mavsdk{Configuration{Camera}};
CameraServer camera_server{mavsdk.default_component()}; // using MAV_COMP_ID_CAMERA1
WinchServer winch_server{mavsdk.component_by_id(MAV_COMP_ID_WINCH)}; // or whatever, if additional componens within a mavsdk server are required.

[julianoes]

Done in #2169.