xfs_repair: don't fail directory repairs when grabbing inodes

xfs_repair: don't fail directory repairs when grabbing inodes

There are a few places where xfs_repair needs to be able to load a
damaged directory inode to perform repairs.  Since inline data fork
verifiers can now be customized, refactor libxfs_iget to enable
repair to get at this so that we don't crash in phase 6.

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>