wifi: mac80211: lock wiphy in IP address notifier

Lock the wiphy in the IP address notifier as another
place that should have it locked before calling into
the driver. This needs a bit of attention since the
notifier can be called while the wiphy is already
locked, when we remove an interface. Handle this by
not running the notifier in this case, and instead
calling out to the driver directly.

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