LU-16796 mdt: Change struct cdt_agent_record_loc to use kref

LU-16796 mdt: Change struct cdt_agent_record_loc to use kref

This patch changes struct cdt_agent_record_loc to use
kref(refcount_t) instead of atomic_t

Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I99141b00b4cfc7b4b46a87462b9ce21735bb0e7d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52153
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>