wsgi server: address family discovery is not quite right

The code introduced to improve binding to an IPv6 address is based on
similar code in Python itself, but is missing some critical arguments to
the socket.getaddrinfo() call: in particular, the socket type must be
set to SOCK_STREAM, because we want a TCP connection; the AI_PASSIVE
flag should also be passed because we intend to use the result for
binding a listen socket rather than making an outbound connection.

Author: jclulow

prometheus_client/exposition.py

@@ -154,7 +154,7 @@ def _get_best_family(address, port):
     # binding an ipv6 address is requested.
     # This function is based on what upstream python did for http.server
     # in https://github.com/python/cpython/pull/11767
-    infos = socket.getaddrinfo(address, port)
+    infos = socket.getaddrinfo(address, port, type=socket.SOCK_STREAM, flags=socket.AI_PASSIVE)
     family, _, _, _, sockaddr = next(iter(infos))
     return family, sockaddr[0]