iwlwifi: apply filter flags directly

Since iwl_configure_filter can now sleep since
the mac80211 callback was changed, we can now
apply filter flags changes directly.

Also, while at it, make the code a bit more
generic with a local macro. There's no need
to check changed_flags since we apply all at
the same time anyway.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>