mkfs.xfs fix sunit size on 512e and 4kN disks.

mkfs.xfs fix sunit size on 512e and 4kN disks.

Creating of XFS on 4kN or 512e disk result in suboptimal LSU/LSUNIT.
As of now we check if the sectorsize is bigger than XLOG_HEADER_SIZE
and so we set lsu to blocksize. But we do not check the the size if
lsunit can be bigger to fit the disk geometry.

Signed-off-by: Lukas Herbolt <lukas@herbolt.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>