MC land detector fix

Make MC land detector more sensitive to LANDED -> IN AIR transitions:

 - Min takeoff throttle (INAV_LAND_THR) changed from 0.3 to 0.2 to work on overpowered systems
 - Altitude change OR (instead of AND) big throttle triggers 'IN AIR' state

This may cause longer delay before triggering 'LANDED' state after landing in alt hold modes. 'IN AIR' will be triggered while vehicle is still on ground, but it should be not too bad.