cfg80211: fix race in netlink owner interface destruction

My previous fix here to fix the deadlock left a race where
the exact same deadlock (see the original commit referenced
below) can still happen if cfg80211_destroy_ifaces() already
runs while nl80211_netlink_notify() is still marking some
interfaces as nl_owner_dead.

The race happens because we have two loops here - first we
dev_close() all the netdevs, and then we destroy them. If we
also have two netdevs (first one need only be a wdev though)
then we can find one during the first iteration, close it,
and go to the second iteration -- but then find two, and try
to destroy also the one we didn't close yet.

Fix this by only iterating once.

Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
Fixes: ea6b2098

 ("cfg80211: fix locking in netlink owner interface destruction")
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20220201130951.22093-1-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>