Add the SIOCSIFMTU ioctl to allow ioctl changes;
Add the SIOCSIFMTU ioctl to allow ioctl changes;

ok brad@ (w/ comments), reyk@

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