xfs/011: support byte-based grant heads are stored in bytes now

xfs/011: support byte-based grant heads are stored in bytes now

New kernels where reservation grant track the actual reservation space
consumed in bytes instead of LSNs in cycle/block tuples export different
sysfs files for this information.

Adapt the test to detect which version is exported, and simply check
for a near-zero reservation space consumption for the byte based version.

Based on work from Dave Chinner.

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