Debian #562126; enable gdmchooser to work with netbase default setting
net.ipv6.bindv6only=1

diff -Naur gdm-2.20.10/gui/gdmchooser.c gdm-2.20.10/gui/gdmchooser.c
--- gdm-2.20.10/gui/gdmchooser.c	2009-03-19 00:29:11.000000000 -0430
+++ gdm-2.20.10/gui/gdmchooser.c	2010-02-09 20:10:08.000000000 -0430
@@ -1121,6 +1121,7 @@
 {
 	static XdmcpHeader header;
 	gint sockopts = 1;
+	int ipv6_only_flag = 0;
 
 	/* Open socket for communication */
 #ifdef ENABLE_IPV6
@@ -1140,6 +1141,13 @@
 		gdm_common_fail_exit ("Could not set socket options!");
 	}
 
+	if (have_ipv6) {
+		if (setsockopt (sockfd, IPPROTO_IPV6, IPV6_V6ONLY,
+			(char*)&ipv6_only_flag, sizeof(ipv6_only_flag)) < 0) {
+			gdm_common_fail_exit ("Could not set socket options!");
+            }
+	}
+
 	/* Assemble XDMCP BROADCAST_QUERY packet in static buffer */
 	header.opcode  = (CARD16) BROADCAST_QUERY;
 	header.length  = 1;