ardupilotmega.xml: report active EKF source sets and lanes

[landswellsong]

Context: ArduPilot/ardupilot#31154

[peterbarker]

Could you add a third field, please, which specifies which estimator type you're using?

So something like AHRS_TYPE and a matching enumeration echoing our AP_AHRS::EKFType enumeration?

That means that if you have fallen back to a different estimator (e.g. DCM) we can tell on the GCS that this has happened.

We run a warning module for our flights in Canberra and we'd definitely check that we're running the estimator we should be!

[landswellsong]

Yup I'm following the devcall silently ;) It can actually be pretty useful for myself too. I have a question though, should the EAHRS/DCM reporting stay as is except for the new flag or should I pass zeroes for lanes etc? I'm passing 1 not to confuse the supposed UI i.e. "we're using the only source set available" and "we're running our only lane". That sounds a little wrong, but so is the whole EKF message on a non EKF estimator.

[landswellsong]

@peterbarker addressed the commit feedback