Because, according to RFC 3493, that will cause getaddrinfo to
overlook the ::1 loopback if there's not some other interface with
a global IPv6 address. The rationale being that the flag helps
prevent unnecessary AAAA lookups, but since I set AI_NUMERICHOST,
lookups aren't going to happen anyway.
Also update the IPv6 Bro communication test to get it to work more
reliably.
