LU-17000 gss: update init_channel initialization

LU-17000 gss: update init_channel initialization

Only root needs write access to 'sptlrpc.gss.init_channel', so adjust
permissions accordingly when sysfs file is created.

Lustre-change: https://review.whamcloud.com/55322
Lustre-commit: TBD (from 44c147a3bdf8d44ef3e36c86018bacacec542341)

DDN-Bug-Id: EX-9705
Test-Parameters: kerberos=true testlist=sanity-krb5
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I6539ade1a9d815664f6659a5c1ee25e7f1f7df0e
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/55320
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>