Boring "BAD AHRS" and "BAD GPS Health" during SITL and X-Plane 11

#### Issue details
During built-in or custom SITL with X-Plane these AHRS errors continue to appear, this obviously clears any other message and is really boring.
AHRS_EFK_TYPE cheating already set to 10, the problem is there anyway.
@meee1, I hope we can find a solution.

https://youtu.be/zOJVnTfiBr8

#### Version

The latest beta

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ x ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Glider

#### Hardware type
SITL
#### Logs
Log is related to the simulated flight in the video

[00000004.ZIP](https://github.com/ArduPilot/MissionPlanner/files/3260525/00000004.ZIP)

Start by reproducing the repeated AHRS and GPS Health messages in the built-in or custom SITL setup with X-Plane 11, using the attached 00000004.ZIP log and linked video as references. Trace why these warnings continue despite AHRS_EFK_TYPE being set to 10, then verify that the warnings no longer continually obscure other messages.

Written by the indexing model from the issue text.