selftests/vm: update hugetlb madvise

Commit 8ebe0a5e ("mm,madvise,hugetlb: fix unexpected data loss with
MADV_DONTNEED on hugetlbfs") changed how the passed length was interpreted
for hugetlb mappings.  It was changed from align up to align down.  The
hugetlb-madvise test explicitly tests this behavior.  Change test to
expect new behavior.

Link: https://lkml.kernel.org/r/20221104011632.357049-1-mike.kravetz@oracle.com
Link: https://lore.kernel.org/oe-lkp/202211040619.2ec447d7-oliver.sang@intel.com


Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>