mac80211: fix a kernel panic when TXing after TXQ teardown

Recently TXQ teardown was moved earlier in ieee80211_unregister_hw(),
to avoid a use-after-free of the netdev data. However, interfaces
aren't fully removed at the point, and cfg80211_shutdown_all_interfaces
can for example, TX a deauth frame. Move the TXQ teardown to the
point between cfg80211_shutdown_all_interfaces and the free of
netdev queues, so we can be sure they are torn down before netdev
is freed, but after there is no ongoing TX.

Fixes: 77cfaf52 ("mac80211: Run TXQ teardown code before de-registering interfaces")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>