mac80211: update ht flag if bss configuration changed

There's a bug in tracking HT opmode changes in mac80211, it
fails to update the driver when the channel parameters don't
change.

Move the code to do the HT opmode checking independently of
the channel/bandwidth tracking.

Signed-off-by: Avri Altman <avri.altman@intel.com>
[edit commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>