git daemon and v6-only

Regarding the following code in daemon.c socksetup():

#ifdef IPV6_V6ONLY
                if (ai->ai_family == AF_INET6) {
                        int on = 1;
                        setsockopt(sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
                                   &on, sizeof(on));
                        /* Note: error is not fatal */
                }
#endif

On Linux this causes you to bind separately to v4 and v6 interfaces, 
avoiding the default (desired) behavior of using a single socket for 
both v4 and v6.

	Jeff