Drain task q items when transitioning to INIT state; this closes a race seen on smp laptops when suspending where the rx task can be entered after the interface is detach'd.
Drain task q items when transitioning to INIT state; this closes a
race seen on smp laptops when suspending where the rx task can be
entered after the interface is detach'd.

NB: use of taskqueue_drain while holding the softc mutex is problematic

Submitted by:	ambrisko
MFC after:	1 month

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