vduse: Requeue failed read to send_list head

vduse: Requeue failed read to send_list head

When copy_to_iter() fails in vduse_dev_read_iter(), put the message back
at the head of send_list to preserve FIFO ordering and retry the oldest
pending request first.

Fixes: c8a6153b6c59 ("vduse: Introduce VDUSE - vDPA Device in Userspace")
Reported-by: Michael S. Tsirkin <mst@redhat.com>
Suggested-by: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Zhang Tianci <zhangtianci.1997@bytedance.com>
Reviewed-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260226115550.1814-2-zhangtianci.1997@bytedance.com>