xfs_db: metadump metadir rt bitmap and summary files

xfs_db: metadump metadir rt bitmap and summary files

Don't skip dumping the data fork for regular files that are marked as
metadata inodes.  This catches rtbitmap and summary inodes on rtgroup
enabled file systems where their inode numbers aren't recorded in the
superblock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>