block/blkio: use blkio_set_int("fd") to check fd support

block/blkio: use blkio_set_int("fd") to check fd support

Setting the `fd` property fails with virtio-blk-* libblkio drivers
that do not support fd passing since
https://gitlab.com/libblkio/libblkio/-/merge_requests/208.

Getting the `fd` property, on the other hand, always succeeds for
virtio-blk-* libblkio drivers even when they don't support fd passing.

This patch switches to setting the `fd` property because it is a
better mechanism for probing fd passing support than getting the `fd`
property.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20230727161020.84213-5-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>