This update applies to pixhawk only

Also one param name in the code clarified.

With H_ prefix they appear with the rest of the tradheli specific params in the parameter list.

This prevents full negative pitch when touching down in Alt Hold or Auto-Landing.

We need the flash space, and this probably won't work for tradheli anyway since tradheli needs most of the control from Feedforward rather than P term.  And D-term is very very bad.