update the commander to only use local pos for landing detection when on...

... rotary wing

Conflicts:
	src/modules/commander/commander.cpp

with #530 the estimator used for fixedwing aircraft publishes local_pos as well. This pull request makes sure that local_pos is only used for quadrocopters in the commander for the takeoff detection (as the fixedwing controller handles this separately)

Tested in fixedwing hil
Needs testing on quadrocopter