Hm, the dnsmasq setting fails after a reboot as the usb0 device is not there at that time.

I resolved this by changing the /etc/event.d/dnsmasq exec line to just

exec /usr/sbin/dnsmasq -k

This will make dnsmas q to listen to the grps/wlan devices too which we probably do not want, but for now that's fine with me...