IMPS / Idle mode power save

[Olof Johansson]

Hey all.

I've worked a bit on the IMPS packets to see if there was anything to
save there.
I've implemented it like this:
https://github.com/Coi-l/wcn36xx/commit/ea6a7e4ac2731b4bc463e9e193949d2d3addc208

I've been doing some measurements with and without the module loaded,
with and without imps functionality turned on and before and after
both a scan and a connect and then disconnect and also ifconfig wlan0
up / down.

Based on my results it looks like the IMPS functionality is a
null-func for the firmware. At least when it comes to measurable power
save results.

I put the phone in flight mode without sim and measured.. in all
scenarios the phone returned to the same baseline which was about 2.3
mA.

My guess is that since the fw knows whether it's connected or not by
itself the IMPS op is no longer needed.

Any thoughts or comments on this or my results?

Otherwise I think we can skip implementing the imps functionality
which is nice. :)


Cheers
--
Olof