mac80211: stop toggling IEEE80211_HT_CAP_SUP_WIDTH_20_40

For VHT, many more bandwidth changes are possible. As a first
step, stop toggling the IEEE80211_HT_CAP_SUP_WIDTH_20_40 flag
in the HT capabilities and instead introduce a bandwidth field
indicating the currently usable bandwidth to transmit to the
station. Of course, make all drivers use it.

To achieve this, make ieee80211_ht_cap_ie_to_sta_ht_cap() get
the station as an argument, rather than the new capabilities,
so it can set up the new bandwidth field.

If the station is a VHT station and VHT bandwidth is in use,
also set the bandwidth accordingly.

Doing this allows us to get rid of the supports_40mhz flag as
the HT capabilities now reflect the true capability instead of
the current setting.

While at it, also fix ieee80211_ht_cap_ie_to_sta_ht_cap() to not
ignore HT cap overrides when MCS TX isn't supported (not that it
really happens...)

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/sta_info.h

@@ -296,8 +296,6 @@ struct sta_ampdu_mlme {
  * @sta: station information we share with the driver
  * @sta_state: duplicates information about station state (for debug)
  * @beacon_loss_count: number of times beacon loss has triggered
- * @supports_40mhz: tracks whether the station advertised 40 MHz support
- *	as we overwrite its HT parameters with the currently used value
  * @rcu_head: RCU head used for freeing this station struct
  */
 struct sta_info {
@@ -403,8 +401,6 @@ struct sta_info {
 	unsigned int lost_packets;
 	unsigned int beacon_loss_count;
 
-	bool supports_40mhz;
-
 	/* keep last! */
 	struct ieee80211_sta sta;
 };