tracker switches into this mode when it receives a do-set-servo command
from the GCS. In this mode the tracker simply moves the servo to the
specified pwm.
these servos are either moving at a constant rate, or off. To really
move them accurately we need to know about this and not use a PID.
This doesn't yet support ballerina, but could do with a bit more work.
AntennaTracker has not been maintained as other parts of the system and
libraries have been modernised. This patch at least gets it to the stage where
it compiles and runs in SITL. Also added Tools/autotest/sim_antennatracker.sh
to run in SITL
Randy Mackay
Andrew Tridgell
Mike McCauley