blkio/drivers/virtio_blk: fail "fd" setting earlier as possible
Currently only virtio-blk-vhost-vdpa
driver supports the "fd"
property. If users set "fd" for other drivers, they will receive an
error only during blkio_connect().
Let's allow the user to check if "fd" is supported or not by the driver earlier as possible, when "fd" is set.
Signed-off-by: Stefano Garzarella sgarzare@redhat.com