xfs_repair: rebuild the metadata directory

xfs_repair: rebuild the metadata directory

Check the dirents in metadata directories for problems and repair them
if necessary.  Also make sure that the sb-rooted inodes (root, metadir
root, rt bitmap, rt summary) are always allocated in that order.

Note that xfs_repair will always rebuild the metadata directory tree
itself, so we only need to report problems, not fix them.

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