mac80211: update sta bw on ht chanwidth action frame

Commit e1a0c6b3

 ("mac80211: stop toggling IEEE80211_HT_CAP_SUP_WIDTH_20_40")
mistakenly removed the actual update of sta->sta.bandwidth.

Refactor ieee80211_sta_cur_vht_bw() into multiple functions
(calculate caps-bw and chandef-bw separately, and min them
with cur_max_bandwidth).

On ht chanwidth action frame set only cur_max_bandwidth
(according to the sta capabilities) and recalc the sta bw.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>