LU-18539 libcfs: introduce OBD_FREE_RCU()

LU-18539 libcfs: introduce OBD_FREE_RCU()

which can be used instead of direct call to kfree_rcu(), does
internal counting for memory leak detector and let us use
regular OBD_ALLOC().

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: I7dfbfb0856440632ef56fbd1ab76e4b5b90b81e9
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57387
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Emoly Liu <emoly@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>