LU-18834 obdclass: check overflow when doing sum in stats

LU-18834 obdclass: check overflow when doing sum in stats

Check overflow when calculating cl_sum and cl_sumsquare in stats.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: Icdf31324ef0f06adc184e6fe5348acad25962d53
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58566
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Zhenyu Xu <bobijam@hotmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>