The addon is currently hosted here: https://github.com/storpool/addon-vnfilter
I believe that this addon that uses the reworked infrastructure in OpenNebula 5.10 is covering at least the following issues:
To cover some cases it is patching the iptables chains generated by OpenNebula using hard-coded offsets so it is suitable/tested for OpenNebula 5.10.0 and 5.10.1. If there are changes in the iptables rules in the future the offsets could be fixed. I hope that the spoofing filters will be fixed upstream and will try to keep the code working until this time.