commander arming: add a grace period of 5 seconds to allow re-arming w/o preflight checks
commander arming: add a grace period of 5 seconds to allow re-arming w/o preflight checks

This changes the arming logic such that the preflight checks don't need
to be satisfied if arming happens < 5 seconds after the last disarming.
This allows to recover from accidental in-air disarming.

acfloria/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,PX4/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,dagar/Firmware,Aerotenna/Firmware,dagar/Firmware,Aerotenna/Firmware,krbeverx/Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,krbeverx/Firmware,dagar/Firmware,krbeverx/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,PX4/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,krbeverx/Firmware,Aerotenna/Firmware,PX4/Firmware,Aerotenna/Firmware,dagar/Firmware