mac80211: Interoperability workaround for 80+80 and 160 MHz channels

mac80211: Interoperability workaround for 80+80 and 160 MHz channels

Number of deployed 80 MHz capable VHT stations that do not support 80+80
and 160 MHz bandwidths seem to misbehave when trying to connect to an AP
that advertises 80+80 or 160 MHz channel bandwidth in the VHT Operation
element. To avoid such issues with deployed devices, modify the design
based on recently accepted IEEE 802.11 standard changes (*).

This allows poorly implemented VHT 80 MHz stations to connect with the
AP in 80 MHz mode. 80+80 and 160 MHz capable stations need to support
the new workaround mechanism to allow full bandwidth to be used.
However, there are more or less no impacted station with 80+80/160
capability deployed.

The rebased version of this patch is based on the updated version from
Johannes Berg to take the HT/VHT chandef refactoring into account.

(*) Changes in
https://mentor.ieee.org/802.11/dcn/15/11-15-1530-04-000m-vht160-operation-signaling-through-non-zero-ccfs1.docx
were accepted during the IEEE 802.11 January 2016 meeting.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>