100% irqreturn_t cleanups

Affected drivers: 3c523, 527, 68360enet, 7990, a2065, am79c961a,
appletalk/{ltpc,cops}, ariadne, {lotsa}lance, au1000_eth, eth16i,
ewrk3, gt96100eth, hamradio/several, ibmlana, ioc3-eth, *-skeleton,
lasi_82596, mac89x0, pcmcia/3c574_cs, rrunner, sb1000, sb1250-mac,
sgiseeq, sk_g16, sk_mca, skfddi, sonic, sun3_82586, tc35815,
tokenring/several, wan/several