ceph: don't use CEPH_OSD_FLAG_ORDERSNAP

Inode can be moved between snap realms. It's possible inode is moved
into a snap realm whose seq number is smaller than old snap realm's.
So there is no guarantee that seq number inode's snap context always
increases.

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>