move the promiscuous mode handling code to sis_setpromisc() and simplify the ioctl handler.
move the promiscuous mode handling code to sis_setpromisc() and simplify
the ioctl handler.

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