Plane: LEDs no longer work since 4.6 BUG

Since I upgraded to version 4.6, the LEDs no longer work.
If I dowgrade to 4.5.7 they work again.

**Version**
4.6

**Platform**
[ ] All
[ ] AntennaTracker
[ ] Copter
[X] Plane
[ ] Rover
[ ] Submarine

**Airframe type**
Flying wing

**Hardware type**
Mateksys F405-WSE

Start by reproducing the LED failure on ArduPlane 4.6 with the flying-wing airframe and Mateksys F405-WSE, then compare it with 4.5.7 where the LEDs work. Identify the regression and verify that the LEDs work again on the affected hardware without breaking the 4.6 Plane configuration.

Written by the indexing model from the issue text.