Build for Netgear R7800

Thanks. I guess it might be merged some day, but clearly not for 22.03. Perhaps just as well, as migrating my old 17-installation will be easier if it is still swconfig. However, the IGMP snooping bug that I reported (and patched for my own use) still hasn't been fixed when using swconfig, but perhaps it would have worked with DSA, since the drivers are entirely different. This bug forces me to build myself, otherwise I could have used the official releases.