fix INRM301 failsafe BUG

[Xy2019]

Fixes #3297

Summary of changes:

[richardclli]

Seems finally got a way to do boardOff properly without entering emergency mode in next power on.

[richardclli]

@raphaelcoeffic Please take a look in the protocol part, @Xy2019 is Flysky's programmer, he will help to fix problems from now on.

[Xy2019]

Seems finally got a way to do boardOff properly without entering emergency mode in next power on.

The last modification would lead to emergency mode, so I re-modified and submitted it.

[richardclli]

@Xy2019 it would be better to split PR so that each PR only fix one issue. Hard to review and merge if mixed together.

[Xy2019]

@Xy2019 it would be better to split PR so that each PR only fix one issue. Hard to review and merge if mixed together.

OK, I tried to resubmit.

[pfeerick]

Seems finally got a way to do boardOff properly without entering emergency mode in next power on.

Not quite... while this mostly works, I naturally found one instance where it still triggers... which is if USB was active (i.e. SD mode) when you power down, it will indeed startup fine and show the charge screen. But the next time the radio powers on, it will EM.

Maybe needs to be handled at the charge screen so that UNEXPECTED_SHUTDOWN() is not true in that edge case. Then again, if it encourages people to NOT power off the radio while the SD card is still mounted (ok, ok, I know this also means joystick mode)... I'm not complaining 😁

@Xy2019 Can you remove the change to board.cpp now as the changes were merged as part of #3325

[pfeerick]

Seems to be working perfectly on EL18 w/ Ftr12B - can now set custom failsafe.