xfs: ensure unlinked list state is consistent with nlink during scrub

xfs: ensure unlinked list state is consistent with nlink during scrub

Now that we have the means to tell if an inode is on an unlinked inode
list or not, we can check that an inode with zero link count is on the
unlinked list; and an inode that has nonzero link count is not on that
list.  Make repair clean things up too.

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