virtio-serial: fix ANY_LAYOUT

Don't assume a specific layout for control messages.
Required by virtio 1.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Reviewed-by: Jason Wang <jasowang@redhat.com>

hw/char/virtio-serial-bus.c

@@ -195,7 +195,8 @@ static size_t send_control_msg(VirtIOSerial *vser, void *buf, size_t len)
         return 0;
     }
 
-    memcpy(elem.in_sg[0].iov_base, buf, len);
+    /* TODO: detect a buffer that's too short, set NEEDS_RESET */
+    iov_from_buf(elem.in_sg, elem.in_num, 0, buf, len);
 
     virtqueue_push(vq, &elem, len);
     virtio_notify(VIRTIO_DEVICE(vser), vq);