After commit 40bad8f3("virtio-net: fix
used len for tx"), async_tx.len was no longer used afterwards. So
remove useless codes with it.
Signed-off-by: NJason Wang <jasowang@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>