For the old ceph version, if it received this one metric message
containing the dentry lease metric info, it will just ignore it.

URL: https://tracker.ceph.com/issues/43423Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>