mac80211: Fix ignored HT override configurations

HT override configurations was ignored when choosing the channel
(until now, the override configuration affected only the
capabilities shown in the IEs).

The override configurations received only on association time,
so in this case we should determine the channel again.

Signed-off-by: Chaya Rachel Ivgi <chaya.rachel.ivgi@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>