LU-12885 mdd: only bottom of clf_flags in changelog

LU-12885 mdd: only bottom of clf_flags in changelog

Make it clear at the callers that only the bottom 12 bits of
clf_flags are stored in the Changelog record.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I23c0844e7ee59dd007b83f37d591df6fbe3ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/36522
Reviewed-by: Aurelien Degremont <adegremont@nvidia.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>