iwlwifi: mvm: BT Coex - track bandwidth changes in HT

BT Coex needs to be updated when the bandwidth is modified
by the AP.
While at it, remove the vif parameter from
bt_coex_vif_change since it was unused.

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