virtio-ring: move queue_index to vring_virtqueue

Instead of storing the queue index in transport-specific virtio structs,
this patch moves them to vring_virtqueue and introduces an helper to get
the value.  This lets drivers simplify their management and tracing of
virtqueues.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 47cccd5..5565af2 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -198,7 +198,7 @@
 	if (err)
 		goto out;
 
-	vq = vring_new_virtqueue(config->num, KVM_S390_VIRTIO_RING_ALIGN,
+	vq = vring_new_virtqueue(index, config->num, KVM_S390_VIRTIO_RING_ALIGN,
 				 vdev, true, (void *) config->address,
 				 kvm_notify, callback, name);
 	if (!vq) {