iwlwifi: mvm: allow to disable beacon filtering for AP/GO interface

When in AP mode we need to filter in beacons from other APs to update HT
operation mode. As a power optimization the beacons are filtered out when
there are no associated stations. As a result, when there are no
associated stations, we will not update the HT operation mode until a
station connects.
Add a debugfs parameter that allows to disable this optimization.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>