PeerIndex names the peer a source address came from, but for two peers
holding the same prefix, which only a default route can be after the
overlap check, it kept the first while amneziawg-go's allowed-IPs table
hands the prefix to the peer configured last. Traffic was then billed
to a different client than the one the device accepted it from.
An equal-length match now goes to the later peer, as in the device.
MHSanaei