AP_InertialSensor: constrain ICM45686 to 800Hz-6.4KHz

[andyp1per]

Simpler alternative to #27573

[bugobliterator]

Hi @andyp1per I don't like this way of doing it actually. This PR changes the ODR of the sensor to a seriously low value, which is quite a regression, and changes filter behaviour and possibly have affect on measurement quality as well. I would really like to continue to find a way to get the initial PR in.

[andyp1per]

@bugobliterator I changed this so the ODR is unchanged for the settings you are concerned about. To get the other PR in please can you make it this simple - I had to write this PR simply to get straight in my head what your PR is actually trying to do - there are so many non-core changes that its really hard to parse and its the non-core changes that I am really objecting to. The actual change you want should be a matter of a few lines.

Note that I am not doing anything different here to what is happening in the ICM42688 which goes from 1KHz - 8Khz (instead of 800Hz - 6.4KHz) the differences are not that significant. The actual sensor rate is still happening at a very high rate so a lot of the aliasing advantages are still there.