Check if interface was stopped before calling rx/tx interrupt routines.
Check if interface was stopped before calling rx/tx interrupt routines.

Report & tests by mxb@alumni.chalmers.se, thanks!
OK deraadt, chris

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars