logged version of di_next_unlinked which is actually always stored in the
correct ondisk format. This was pointed out to us by Shailendra Tripathi.
And is evident in the xfs qa test of 121.

SGI-PV: 953263
SGI-Modid: xfs-linux-melb:xfs-kern:26044a
Signed-off-by: NTim Shimmin <tes@sgi.com>
Signed-off-by: NNathan Scott <nathans@sgi.com>