Forward port ath9k.diff patch to kernel 6.12

[wirelessOJ]

From: raspberrypi/linux#4358 (comment)

Almost all of that forward ports with minimal intervention.

The only bit that doesn't is the adjfreq hook has been merged into a adjfine, and been removed with raspberrypi/linux@75ab70e.
There are a number of other conversions from adjfreq to adjfine for various cards (raspberrypi/linux@d8fae25, raspberrypi/linux@5a55423, raspberrypi/linux@ccd3bf9, raspberrypi/linux@3626a69, etc), but I know nothing about that API or hardware to be immediately able to do the conversion.

I've thrown the basic forward port to 6.12 at raspberrypi/linux#6882, but I am NOT proposing that this would be merged into our tree.
The function of adjfine has been disabled with #if 0, so needs fixing up in order to get PTP to work.

The first test would be to see if that works at all without PTP to confirm that no other parts are broken. If everything appears to be working, then someone with a little more knowledge or time could look into the implementation of that function.

---Does anyone have knowledge on this final component?