Fix missing knob to properly disable IPv6 support when headers lack it.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura libupnp-1.6.15/upnp/src/ssdp/ssdp_device.c libupnp-1.6.15-noipv6/upnp/src/ssdp/ssdp_device.c
--- libupnp-1.6.15/upnp/src/ssdp/ssdp_device.c	2011-11-04 19:33:59.000000000 -0300
+++ libupnp-1.6.15-noipv6/upnp/src/ssdp/ssdp_device.c	2012-03-20 21:00:26.274098343 -0300
@@ -199,6 +199,7 @@
 		setsockopt(ReplySock, IPPROTO_IP, IP_MULTICAST_TTL,
 			   (char *)&ttl, sizeof(int));
 		socklen = sizeof(struct sockaddr_in);
+#ifdef UPNP_ENABLE_IPV6
 	} else if (DestAddr->sa_family == AF_INET6) {
 		inet_ntop(AF_INET6,
 			  &((struct sockaddr_in6 *)DestAddr)->sin6_addr,
@@ -207,6 +208,7 @@
 			   (char *)&gIF_INDEX, sizeof(gIF_INDEX));
 		setsockopt(ReplySock, IPPROTO_IPV6, IPV6_MULTICAST_HOPS,
 			   (char *)&hops, sizeof(hops));
+#endif
 	} else {
 		UpnpPrintf(UPNP_CRITICAL, SSDP, __FILE__, __LINE__,
 			   "Invalid destination address specified.");