wifi: rtl8xxxu: gen2: Enable 40 MHz channel width

The module parameter ht40_2g was supposed to enable 40 MHz operation,
but it didn't.

Tell the firmware about the channel width when updating the rate mask.
This makes it work with my gen 2 chip RTL8188FU.

I'm not sure if anything needs to be done for the gen 1 chips, if 40
MHz channel width already works or not. They update the rate mask with
a different structure which doesn't have a field for the channel width.

Also set the channel width correctly for sta_statistics.

Fixes: f653e690 ("rtl8xxxu: Implement basic 8723b specific update_rate_mask() function")
Fixes: bd917b3d

 ("rtl8xxxu: fill up txrate info for gen1 chips")
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Acked-by: Jes Sorensen <jes@trained-monkey.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/3a950997-7580-8a6b-97a0-e0a81a135456@gmail.com