LinuxKPI: 802.11: improve queue locking

Introduce an internal lkpi_ieee80211_wake_queues_locked() function
that can be used from context holding the wiphy lock.
Make linuxkpi_ieee80211_wake_queues() a wrapper with locking around
this.

Equally apply the wiphy lock to linuxkpi_ieee80211_wake_queue().

In lkpi_ieee80211_wake_queues() only wakeup the driver if the queue
is not empty; otherwise weird sideeffects can happen with some drivers.

Sponsored by: The FreeBSD Foundation
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