mac80211: recalc min_def chanctx even when chandef is identical

The min_def chanctx is affected not only by the current chandef, but
sometimes also by other stations on the vif. There's a valid scenario
where a TDLS peer can widen its BW, thereby causing the min_def
to increase.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>