Transponder tab does not support Sagetech XP transponders for operating messages

#### Issue details
The transponder tab will not send any operating messages from the flight controller to an XPS-TR transponder, but GPS data is being sent through, and if the transponder is set to ALT mode from Sagetech's Engineering GUI, ADSB information is showing up on the flight data screen.

Pictured: Valid GPS messages being sent to and from the flight controller and transponder despite no operating messages appearing when using a logic analyzer

Pictured: Correct ADSB information after setting operating mode externally through another program

#### Version
1.3.80

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ X ] Plane
[ ] Rover
[ ] Sub

#### Hardware type
CubeOrange
Sagetech XPS-TR

Start in the Mission Planner transponder tab and reproduce the issue with a CubeOrange and Sagetech XPS-TR on Plane 1.3.80, comparing operating messages with the GPS traffic using a logic analyzer. Done means operating messages reach the transponder and ADSB information appears without setting ALT mode externally.

Written by the indexing model from the issue text.