xfs: scrub while appending to a file

xfs: scrub while appending to a file

It turns out that there was a bug in xfs_bmap_count_blocks wherein
the block count returned would count or not count delalloc blocks
depending on the fork format.  This is a bug that is easily exposed
via scrub, so check the output of that function here -- the buggy
version of the function produces online fsck errors.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>