cfg80211: call cfg80211_destroy_ifaces() with wiphy lock held

This is needed since it calls into the driver, which must have the
same context as if we got to destroy an interface through nl80211.
Fix this, and add a direct lockdep assertion so we don't see it
pop up only when the driver calls back to cfg80211.

Fixes: a05829a7

 ("cfg80211: avoid holding the RTNL when calling the driver")
Reported-by:  <syzbot+4305e814f9b267131776@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/20210128183454.d31df9cbd7ce.I1beb07c9492f0ade900e864a098c57041e7a7ebf@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>