LU-11330 osd-zfs: hash for ./.. must be 0

LU-11330 osd-zfs: hash for ./.. must be 0

do not use current iterator position as hash source for dot and dotdot.
instead just return 0 as hash for these entries.

Change-Id: I5ee439b237e8ed98d295f5672b1d0e8a6b48a55b
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34098
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>