- introduce drbr_needs_enqueue that returns whether the interface/br needs
an enqueue operation: returns true if altq is enabled or there are
already packets in the ring (as we need to maintain packet order)
- update all drbr consumers
- fix drbr_flush
- avoid using the driver queue (IFQ_DRV_*) in the altq case as the
multiqueue consumer does not provide enough protection, serialize altq
interaction with the main queue lock
- make drbr_dequeue_cond work with altq
Discussed with: kmacy, yongari, jfv
MFC after: 4 weeks
193cbc4d24