iwlwifi: mvm: fix the ACK / CTS kill mask upon RSSI event

If a vif's RSSI gets good enough, we can enable reduced
Tx power. If so, we need to update the ACK / CTS kill mask
accordingly. Since the auditing for the interfaces was bad,
we enabled reduced Tx power, but didn't update the ACK / CTS
kill mask.
This is harmless since the firmware is most likely to
discard this setting anyway, but it is a good practice
to update it.

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