httpd: fix address family for reverse proxy client socket

httpd: fix address family for reverse proxy client socket

When httpd proxies a request to another server, it first creates
an AF_INET socket, then resolves the server name to a sockaddr,
then connects to it. This fails if the server name resolves to
an IPv6 address.

This patch ensures that the socket is created with the correct
address family (AF_INET6 if the server resolves to an IPv6 address
and AF_INET otherwise).

Signed-off-by: Laurent Bercot <ska-dietlibc@skarnet.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>