mds: only set smaller flag in setattr completion if actually truncating
mds: only set smaller flag in setattr completion if actually truncating

Otherwise we can erroneously trigger the truncation code when another
setattr overlaps with an in-progress truncate.

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph