Make sure wifi interfaces are not soft blocked when they come available

Wifi cards on some laptop models seem to be soft blocked by default which confused users. Add a udev rule to call "rfkill unblock wifi" when new network interfaces are initialised. This needs to be called also for ethX devices as some wifi interfaces use eth in their naming. Better filter should be doable, but this works for now. In addition to dynamic calling, call rfkill also from /etc/rc.local to make sure that it's called at least once during the boot. If the interface does not exist at this point, it has no effect, though.