AP_Periph arm timeout bug

[robertlong13]

Cherry picking the arm timeout feature was incomplete. Was causing the motor to stop every 2s periodically.

[robertlong13]

@loki077 I had to force-push a fix real quick because I was using #if instead of #ifdef for HAL_PERIPH_ARM_MONITORING_ENABLE.

Did we go the #ifdef route to avoid needing to put

#ifndef HAL_PERIPH_ARM_MONITORING_ENABLE
 # define HAL_PERIPH_ARM_MONITORING_ENABLE          0
#endif

in a couple places?

This implementation will cause unexpected results if someone defines HAL_PERIPH_ARM_MONITORING_ENABLE 0 in the hwdef for testing or something. Not a big deal in the near-term, especially for this cherry-pick of the functionality, but I wanted to flag that.

[loki077]

Thanks for finding the missing piece. @robertlong13

will discuss the point you mentioned tomorrow in the office.