Improve MAVLink behavior with flow control capable links

[MUSTARDTIGERFPV]

With these changes, INAV can now be used with ExpressLRS MAVLink, including both RC & telemetry all in one!

You can watch a demo here: https://www.youtube.com/watch?v=d55q5sUbIkc

This should be solid for both ELRS and other MAVLink telemetry radios, though I haven't tested with them yet. Wanted to get the PR created so folks can take a look at it. :)

[mmosca]

Did some basic testing and appears to be working. Will test a bit more and verify telemetry info is getting through.

[mmosca]

Mention change of default values for the mavlink message rates on release notes and that mavlink radio_status messages will ignore half duplex frame pacing and rely on txbuffer.

Transparent radio links will still behave as they did before, by default.

[sugatovo]

The other day I tested expresslrs mavlink on the inav and I want to share my observations. I want to say right away that I have just begun to work with GCS apps, mavlink, autonomous stuff and personal observations are all that I can provide at the moment. Now to the point.

elrs mavlink and ainav 8.0.0. Since I have a laptop from Apple, I am using QgroundControl as the GCS app. Connection between plane and QGC did not cause any problems, in this regard, everything went smoothly. The application itself perfectly tracks the the aircraft and its telemetry, however, when trying to load mission into the aircraft, an error constantly occurs. Various missions such as the Corridor Scan or Survey did not give any results and could not be flashed to FC, so QGC was used only for monitoring params and position. Next, I connected plane to mission planner and everything was more successful. Connection also did not cause any problems, it was enough to follow instructions from this link: https://www.expresslrs.org/software/mavlink/. Mission Planner made it possible to load mission into the flight controller and everything went well. However, you can't download anything other than a waypoint mission. When trying to loiter a point or land plane, Inav performs a return to home and does not want to do programmed mission (even though it was successfully uploaded to the plane) . At the moment, that's it. I will continue to try to figure out how it all works and do updates if I’ll come up with smth.