kclient: fix non-dcache readdir offset calculation
kclient: fix non-dcache readdir offset calculation

Needs to factor in frag_is_leftmost to account for . and .., just
like the fi->offset calculation in readdir_prepopulate.  Fixes the
problem where an ls on a large dir returns duplicate entries.

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