cfg80211: pmsr: fix abort locking

When we destroy the interface we already hold the wdev->mtx
while calling cfg80211_pmsr_wdev_down(), which assumes this
isn't true and flushes the worker that takes the lock, thus
leading to a deadlock.

Fix this by refactoring the worker and calling its code in
cfg80211_pmsr_wdev_down() directly.

We still need to flush the work later to make sure it's not
still running and will crash, but it will not do anything.

Fixes: 9bb7e0f24e7e ("cfg80211: add peer measurement with FTM initiator API")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/core.c b/net/wireless/core.c
index 623dfe5..b36ad8e 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -1068,6 +1068,8 @@ static void __cfg80211_unregister_wdev(struct wireless_dev *wdev, bool sync)
 
 	ASSERT_RTNL();
 
+	flush_work(&wdev->pmsr_free_wk);
+
 	nl80211_notify_iface(rdev, wdev, NL80211_CMD_DEL_INTERFACE);
 
 	list_del_rcu(&wdev->list);