mac80211: fix drv_config_iface_filter() behaviour

There are two bugs with this, first, it shouldn't be called
on an interface that's down, and secondly, it should then be
called when the interface comes up.

Note that the currently only user (iwlwifi) doesn't seem to
care about either of these scenarios.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20200417111830.401d82c7a0bf.I5dc7d718816460c2d8d89c7af6c215f9e2b3078f@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>