xfs: disable the agi rotor for metadata inodes

xfs: disable the agi rotor for metadata inodes

Source kernel commit: 8651b410ae781cc607159c51dbb0b317b23543b1

Ideally, we'd put all the metadata inodes in one place if we could, so
that the metadata all stay reasonably close together instead of
spreading out over the disk.  Furthermore, if the log is internal we'd
probably prefer to keep the metadata near the log.  Therefore, disable
AGI rotoring for metadata inode allocations.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>