We modify the request by adding an offset to vmstate. Let's check the
modified request. It will help us to safely move .bdrv_co_preadv_part
and .bdrv_co_pwritev_part to int64_t type of offset and bytes.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210903102807.27127-3-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>