iwlwifi: mvm: add multicast filtering support

Configure the fw to filter multicast according to
the addresses given by mac80211.

Note that bssid should be given even if we want
to pass all the multicast frames.

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