examples/vhost: use burst enqueue and dequeue from lib
examples/vhost: use burst enqueue and dequeue from lib

In switch_worker and virtio_tx_local, rte_vhost_enqueue_burst is called to
push host packets to guest VM.
Before enqueue packets to guest VM, vhost example uses configure-able retry logic
to wait for enough vring entries.
In switch_worker, rte_vhost_dequeue_burst is called to get packets from guest VM,
then virtio device will be bound to a queue in VMDQ for the first transmitted
packet.

Signed-off-by: Huawei Xie <3b3be4428106761300a2ee559c9f71ecdb091553@intel.com>
Acked-by: Changchun Ouyang <593bf1f161e79772915ea885e47cf0e95f4498c0@intel.com>

phermansson/dpdk,phermansson/dpdk,phermansson/dpdk,phermansson/dpdk