LinuxKPI: 802.11: ensure to select the correct channel width

If HT is enabled but not using CHW=40 set CHW=20 to make sure we do
not get stuck on any other value.

If VHT and the VHT Operation element Channel Width field is 0
(use 20/40) do not update the bandwidth but stick with what HT selected.
This is better than disabling VHT alltogether for 20/40 and allows us
to work on VHT20 and VHT40 APs it seems.
We will have to do more work to can align with the chanctx or deal with
Operating Mode Notification Action frames in LinuxKPI or net80211.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days