This helps Starlight Re:Volver which otherwise usually shows black screen only (through fixing GetBestRoute() for ipv4 loopback address).
/proc/net/route doesn't have entries for loopback. They are also absent in AF_NETLINK socket output, as far as my brief check goes. It is probably possible to see them someone else (e. g., /proc/net/fib_trie) but trying to do so looks like a pointless exercise to me: we can just return forward rows for loopback with the parameters matching Windows as soon as loopback interface is available and we can get an index for it.
The last patch is unrelated, it is just without that nsi/tests crash on up to date Win11 here.