LU-12670 osd-ldiskfs: Shrink rcu critical section

LU-12670 osd-ldiskfs: Shrink rcu critical section

Drop ENTRY/EXIT macros to exclude them rcu critical section
scope without introducing additional work around logic.

Cray-bug-id: LUS-7771
Signed-off-by: Shaun Tancheff <stancheff@cray.com>
Change-Id: I70486ba137592d1a57bc712837b8a300b8017a36
Reviewed-on: https://review.whamcloud.com/35805
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>