OK, I will give it a go although I don't understand how that is related.
For completeness the Network setup I'm after is like the below
Maybe it's a better idea to put the Netgear Switch before the OpenWRT. Then all ethernet devices are send to Netgear Switch which has support for VLAN.20 and VLAN.40 and OpenWRT is only managing the Wireless clients with different networks and only VLAN trunking on one port (no ethernet clients). I guess that's my summer project