iwlwifi: mvm: protect TDLS discovery session

Use the new mac80211 callback to protect a TDLS discovery session so we
can hear the discovery-response packet.

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