As members of the Stooges, Iggy Pop and the Asheton brothers (Ron and Scott) made the most brutally raw and intense album in rock history: 1970's ''Fun House.'' The good news is, they're playing together again on ''Skull Ring.'' The bad news is, on only four tracks. The rest of Ring finds Pop working with a variety of other bands (Green Day, Sum 41), giving the whole thing a scattered feel. But when Iggy and the Ashetons buzz through tunes like ''Little Electric Chair'' (with hand claps!) and the pounding title track, I definitely feel all right.