Implements in-order handling for the virtio-net device.

Since virtio-net utilizes batching for its Rx VirtQueue, the device is
responsible for calling virtqueue_flush once it has completed its
batching operation.

Note:
-----
It's unclear if this implementation is really necessary to "guarantee"
that used VirtQueueElements are put on the used ring in-order since, by
design, virtio-net already does this with its Rx VirtQueue.

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
---
 hw/net/virtio-net.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 9959f1932b..b0375f7e5e 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2069,7 +2069,11 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
 
     for (j = 0; j < i; j++) {
         /* signal other side */
-        virtqueue_fill(q->rx_vq, elems[j], lens[j], j);
+        if (virtio_vdev_has_feature(vdev, VIRTIO_F_IN_ORDER)) {
+            virtqueue_order_element(q->rx_vq, elems[j], lens[j], j, 0);
+        } else {
+            virtqueue_fill(q->rx_vq, elems[j], lens[j], j);
+        }
         g_free(elems[j]);
     }
 
-- 
2.39.3