count how many times ifiqs enqueue and dequeue packets.

count how many times ifiqs enqueue and dequeue packets.

network cards try to enqueue a list of packets on an ifiq once per
interrupt and ifiqs already count how many packets they're handling.
this let's us see how well interrupt mitigation is working on a
ring or interface. ifiqs are supposed to provide backpressure
signalling to a driver if it enqueues a lot more work than it's
able to process in softnet, so recording dequeues let's us see this
ratio.