xfs_repair: dont check metadata directory dirent inumbers

xfs_repair: dont check metadata directory dirent inumbers

Phase 6 always rebuilds the entire metadata directory tree, and repair
quietly ignores all the DIFLAG2_METADATA directory inodes that it finds.
As a result, none of the metadata directories are marked inuse in the
incore data.  Therefore, the is_inode_free checks are not valid for
anything we find in a metadata directory.

Therefore, avoid checking is_inode_free when scanning metadata directory
dirents.

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