Treat the num_queues field as virtio-endian. On big-endian hosts the
vhost-user-blk num_queues field was in the wrong endianness.

Move the blkcfg.num_queues store operation from realize to
vhost_user_blk_update_config() so feature negotiation has finished and
we know the endianness of the device. VIRTIO 1.0 devices are
little-endian, but in case someone wants to use legacy VIRTIO we support
all endianness cases.

Cc: qemu-stable@nongnu.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20210223144653.811468-2-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>