mac80211: support VHT capability overrides

Support the cfg80211 API to override VHT capabilities
on association.

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

diff --cc net/mac80211/ieee80211_i.h
Simple merge

diff --cc net/mac80211/main.c
Simple merge

diff --cc net/mac80211/mlme.c
Simple merge

diff --cc net/mac80211/vht.c
Simple merge