SITL: SIM_GPS_DISABLE should work when AHRS_EKF_TYPE = 10

[rmackay9]

When AHRS_EKF_TYPE = 10 (SITL) the SIM_GPS_DISABLE parameter doesn't have the expected result (which is that the EKF should fail to produce a position estimate).

[peterbarker]

The "perfect" EKF type, 10, doesn't rely on sensors for data, it is just echoing back the simulation numbers. There's going to be a lot of things we'll ignore - all of the simulated sensor "dirtying" parameters, for example. SIM_GPS_DISABLE is just the most obvious one.

We could add a set of flags to allow for changes in EKF-type-10's output?

[rmackay9]

Thanks @peterbarker. I agree this could be a very large tasks so we should consider if it is worth the effort or if the user who reported this can perhaps find another solution instead.