LU-10030 hsm: make changelog flag argument an enum

Since the changelog record flag is being stored on disk, pass it
around as an enum instead of a signed int.  Also make it clear at
the caller that only the low 12 bits of the flag are normally
being stored in the changelog records, since this isn't obvious
to the reader.  For open and close records, the bottom 32 bits
of open flags are recorded.

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ie676fb6bfd3661645dde845fd9ca8bad283ebbe5
Reviewed-on: https://review.whamcloud.com/32112
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>