LU-15252 mdc: add client tunable to disable LSOM update

LU-15252 mdc: add client tunable to disable LSOM update

It seems that mdt_lsom_update() has a serious issue with a single
shared file because of its mdt-level mutex for every close request.
The patch adds mdc_lsom parameter to mdc, base on it state client
sends or not LSOM updates to MDT. By default LSOM is on.

lctl set_param mdc.*.mdc_lsom=[on|off]

For a configuration when LSOM is not used the patch helps
MDT with load avarage with a specific load when many threads
open/read/close for a single file.

HPE-bug-id: LUS-10604
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: Iba0e745a94825641da6b0a1c09488b1e2f54658b
Reviewed-on: https://review.whamcloud.com/45619
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@hpe.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>