[XFS] Make xfs_bulkstat() to report unlinked but referenced inodes

We need xfs_bulkstat() to report inode stat for inodes with link count
zero but reference count non zero.

The fix here:

http://oss.sgi.com/archives/xfs/2007-09/msg00266.html

changed this behavior and made xfs_bulkstat() to filter all unlinked
inodes including those that are not destroyed yet but held by reference.

The attached patch returns back to the original behavior by marking the
on-disk inode buffer "dirty" when di_mode is cleared (at that time both
inode link and reference counter are zero).

SGI-PV: 972004
SGI-Modid: xfs-linux-melb:xfs-kern:29914a

Signed-off-by: Vlad Apostolov <vapo@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>