[XFS] Drop unneeded endian conversion in bulkstat and start readahead for

batches of inode cluster buffers at once, before any blocking reads are
issued.

SGI-PV: 944409
SGI-Modid: xfs-linux-melb:xfs-kern:26606a

Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>