EX-8130 lipe: Add directory scan structs

EX-8130 lipe: Add directory scan structs

This patch adds new structures to lipe_scan3 for collecting
and storing directory statistics, as well as initialization
and destroy functions. This patch is the first in a series
of patches that add functionality for collecting directory
statistics in lipe_find3.

Test-Parameters: trivial
Signed-off-by: Vitaliy Kuznetsov <vkuznetsov@ddn.com>
Change-Id: Ib14ce13677d93d1a53299501138e78c7b290793c
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53958
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexandre Ioffe <aioffe@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>