iwlwifi: mvm: specify filter flags in monitor mode

In firmware "listener" (monitor) mode, we still need to
open up the filters with the filter flags to receive all
frames.

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