alf_queue_bench: micro benchmark multi enqueues before dequeues

This micro benchmark does multiple enqueues before dequeues.

The idea for the pattern originates from how some NIC drivers
cleanup their HW ring queue, in chunks of packets.

Doing this one element at a time, is not optimal usage of the API
given the alf_queue supports bulking, but this test is just an
attempt of exercising more of array data.

Results from CPU E5-2695:

Type:ALF-multi Per elem: 33 cycles(tsc) 13.576 ns (step:128)
 - (measurement period time:0.347569514 sec time_interval:347569514)
 - (invoke count:25600000 tsc_interval:868922934)

Showing the cost is currently : 13.576 ns (33 cycles(tsc))
DPDK ported ring_queue variant: 12.690 ns (31 cycles(tsc))

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>