xfs_repair: implement custom ifork verifiers

xfs_repair: implement custom ifork verifiers

There are a few cases where an early stage of xfs_repair will write an
invalid inode fork buffer to signal to a later stage that it needs to
correct the value.  This happens in phase 4 when we detect an inline
format directory with an invalid .. pointer.  To avoid triggering the
ifork verifiers on this, inject a custom verifier for phase 6 that lets
this pass for now.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>