fsck.gfs2: use gfs2_meta_inval vs. gfs2_inval_inode
    
    This patch removes the vestigial gfs2_journal_blk and reuses it
    for a new gfs2_inode_invalid.  This allows the code to keep better
    track of invalid inodes rather than other invalid metadata.  For
    invalid inodes, there may be cases where we want to invalidate its
    metadata list.  We can't do that for other kinds of metadata like
    invalid eattrs.
    
    rhbz#455300