for the same purpose (ignoring invalid interrupts).
For cards that are not able to stop all interrupts (or we don't know a way
to do that in software, at least) run the clearirq callback even when
ignoring an interrupt because we are not enabled. Otherwise the card would
stop interrupting.
Reserve a driver specific callout handle and an int value in the generic
isic_softc to allow card drivers to implement fancy blinkenlights.