- always check system field for validity
- reject any data outside of "servo position" valid range from Spektrum specification
- properly support XPlus channels (12+)
- debug message if channel count changes
RC Failsafe isn't triggered when PPM signal is valid. These changes
update Failsafe trigger logic for RC input. RF Modules keep sending
valid PPM signal when the RC Transmitter is lost.
RF Modules which are in the air send PPM signal with same type when lost
the signal from ground.