iwlwifi: mvm: BT Coex - set low latency vif as primary

If a vif is in low latency mode, it should be in primary
channel.
Also tell BT Coex about the change when a vif enters or
exits low latency mode.

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