xfs_scrub: retry scrub (and repair) of items that are ok except for XFAIL

xfs_scrub: retry scrub (and repair) of items that are ok except for XFAIL

Sometimes a metadata object will pass all of the obvious scrubber
checks, but we won't be able to cross-reference the object's records
with other metadata objects (e.g. a file data fork and a free space
btree both claim ownership of an extent).  When this happens during the
checking phase, we should queue the object for a repair, which means
that phase 4 will keep re-evaluating the object as repairs proceed.
Eventually, the hope is that we'll fix the filesystem and everything
will scrub cleanly; if not, we recommend running xfs_repair as a second
attempt to fix the inconsistency.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>