xfs_repair: truncate and unmark orphaned metadata inodes

xfs_repair: truncate and unmark orphaned metadata inodes

If an inode claims to be a metadata inode but wasn't linked in either
directory tree, remove the attr fork and reset the data fork if the
contents weren't regular extent mappings before moving the inode to the
lost+found.

We don't ifree the inode, because it's possible that the inode was not
actually a metadata inode but simply got corrupted due to bitflips or
something, and we'd rather let the sysadmin examine what's left of the
file instead of photorec'ing it.

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