feat(radio): Discover SBUS trainer availability (#4266)

Co-authored-by: raphaelcoeffic <1050031+raphaelcoeffic@users.noreply.github.com>
Co-authored-by: Peter Feerick <peter.feerick@gmail.com>

radio/src/tests/mixer.cpp

@@ -848,7 +848,7 @@ TEST(Trainer, UnpluggedTest)
   g_model.mixData[0].weight = 100;
   g_model.mixData[0].delayUp = 50;
   g_model.mixData[0].delayDown = 50;
-  trainerInputValidityTimer = 0;
+  trainerSetTimer(0);
   trainerInput[0] = 1024;
   CHECK_DELAY(0, 5000);
 }