kclient: fix up writes, reads for new op structure
kclient: fix up writes, reads for new op structure

Make sure osdc_readpages still returns bytes read, even though the
overall message result does not (pull it from the op.length).

Set MODIFY flag.

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