xfs: test unlinked inode list checking and repair with loops

Simple test of various weird ways we can screw up unlinked inode list
reconstruction.

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