net/virtio: rationalize queue flushing
net/virtio: rationalize queue flushing

Use the same kind of loop than in virtio_free_queues() and factorize
common code.

Signed-off-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>
Acked-by: Yuanhan Liu <5219796f50b7b6a5f4ac3e8f0a0f9501ee64a87c@fridaylinux.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk