LU-11407 obdclass: init osc.*.rpc_stats start_time

LU-11407 obdclass: init osc.*.rpc_stats start_time

Add missing start_time initialization for osc.*.rpc_stats.

Test-Parameters: trivial
Fixes: ea2cd3af7b ("LU-11407 obdclass: add start time to stats files")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I998b5337ccebc4d3ec18260d259f39c7893ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50734
Reviewed-by: Feng Lei <flei@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>