Change failsafe message to be more generic

Since the MAV_STATE_CRITICAL bit is set for any fail-safe type the message must be more generic.c
https://github.com/diydrones/ardupilot/blob/d130f0c4994f5e33f07364be8e4972adfd1fa723/ArduCopter/GCS_Mavlink.pde#L48-L51

This relates to #978