LU-13601 llite: avoid needless large stats alloc

LU-13601 llite: avoid needless large stats alloc

Allocate the ll_rw_extents_info (5896 bytes), ll_rw_offset_info
(6400 bytes), and ll_rw_process_info (640 bytes) structs only
when these stats are enabled, which is very rarely.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I59bbfce8d7f2422d810617d5fa712a67333ebbe5
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Reviewed-on: https://review.whamcloud.com/40901
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>