LU-10224 obd: free obd_svc_stats when all users are gone

LU-10224 obd: free obd_svc_stats when all users are gone

During object device shutdown obd_svc_stats must only be freed
after all access methods from user-land are no longer possible
to prevent any race and further crash.

Lustre-change: https://review.whamcloud.com/30249
Lustre-commit: ffc843a0aacd78495b1cff51344aaee3e32fc2de

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Iea4f5b0486779c1721c90f32538af1a723f76a79
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Minh Diep <minh.diep@intel.com>
Reviewed-on: https://review.whamcloud.com/31197
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>