mixer function RC: output disarmed value with no valid RC input

[MaEtUgR]

Solved Problem

I received the report from @fury1895 that when:

• mapping a servo to an RC input e.g. aux1
• enabling COM_PREARM_MODE
• Not connecting any RC
  the servo goes to the center position instead of the configured disarmed position.

Solution

I agree that this is unexpected and suggest that actuators mapped to and RC input directly get commanded their disarmed output whenever the RC input is not available (anymore).

Changelog Entry

Bugfix
Documentation: mention this behavior explicitly under https://docs.px4.io/main/en/config/actuators.html#output-functions

Alternatives

We could keep the last valid RC input instead but it's not only more complicated I also currently don't exactly see what use case would require this behavior.

Test coverage

This was not tested. Please @fury1895 test and give feedback.