Something changed in the getaddrinfo() mechanism, causing AF_UNSPEC
in combination with ai_socktype=0 to return IPv4 addresses first
(instead of starting with IPv6 addresses). As a consequence, IPv6
servers are restricted to only IPv4 connections - IPv6 clients will
receive an ICMPv6 error message, which gets translated into an annoying
"protocol error" locally.
The fix is to pretend to be UDP instead of DCCP (pretending to be TCP
also works). This allows getaddrinfo to look up the address without
side effects and has been found to work.