OK, solved via systemd / systemctl 
I created the following service file /etc/systemd/system/WOL-eth0.service
[Unit]
Description=Wake-on-LAN for eth0
Requires=network.target
After=network.target
[Service]
ExecStart=/usr/sbin/ethtool -s eth0 wol g
Type=oneshot
[Install]
WantedBy=multi-user.target
than enabled and started it
systemctl enable WOL-eth0
systemctl start WOL-eth0
After reboot Wake-on ist now set to g
Hope that helps, if anybody wants to use WOL too.
regards
Andreas