A while back I wrote an FPGA-based minimal network stack to work with the MRMAC hard IP of an AMD VC1902 with basically the same functionality: ARP, IPv4, ICMP Echo reply and UDP send/receive. I added the bare bare minimum to get UDP GRO working on the receiver side (Linux).

I also enjoyed the learning experience and works perfectly fine at up to 100G. But I definitely appreciate that I didn't have to go through the same pain under Linux where this stuff just works.