[rotorcraft] motor_mixing: bound the maximum offset in case of saturation
- defaults to a third of the max command
- to change the default define MOTOR_MIXING_MAX_SATURATION_OFFSET
Should improve handling as per issue #385
Merge pull request #386 from flixr/motor_mixing_max_saturation_offset

[rotorcraft] motor_mixing: bound the maximum offset in case of saturation