vhost: use queue id instead of constant ring index

vhost: use queue id instead of constant ring index

Do not use VIRTIO_RXQ or VIRTIO_TXQ anymore; use the queue_id
instead, which will be set to a proper value for a specific queue
when we have multiple queue support enabled.

For now, queue_id is still set with VIRTIO_RXQ or VIRTIO_TXQ,
so it should not break anything.

Signed-off-by: Changchun Ouyang <changchun.ouyang@intel.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Huawei Xie <huawei.xie@intel.com>