LU-13783 libcfs: don't depend on sysctl support for debugfs

LU-13783 libcfs: don't depend on sysctl support for debugfs

Since Linux v5.8-rc1~55^2~6 sysctl support routines like
proc_dointvec() expect a pointer to kernel-space, not userspace.

So stop using these function for debugfs files, and instead
provide bespoke functions.

Lustre-change: https://review.whamcloud.com/40832
Lustre-commit: d707b390aec5e95a1aec9910fb3c8248c231cbfb

Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I340a748bbfbd066054a73299ce32698aa39a0e2d
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-on: https://review.whamcloud.com/43646
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>