LU-12542 osd: consolidate RCU handling

LU-12542 osd: consolidate RCU handling

Consolidate lu_object_header_fini() and kfree_rcu() into a
single lu_object_header_free() function so that callers
which do not need a container for lu_object_header can
avoid duplicating common RCU and OBD_FREE handling code.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I0fa68f11b5008ede5a498d38b69ccaeecf3ebbe5
Reviewed-on: https://review.whamcloud.com/40204
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Ben Evans <beevans@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>