[IPV6] MROUTE: Support multicast forwarding.

Based on ancient patch by Mickael Hoerdt
<hoerdt@clarinet.u-strasbg.fr>, which is available at
<http://www-r2.u-strasbg.fr/~hoerdt/dev/linux_ipv6_mforwarding/patch-linux-ipv6-mforwarding-0.1a>.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
index 47263e4..9a2ea81 100644
--- a/net/ipv6/Kconfig
+++ b/net/ipv6/Kconfig
@@ -209,3 +209,10 @@
 
 	  If unsure, say N.
 
+config IPV6_MROUTE
+	bool "IPv6: multicast routing (EXPERIMENTAL)"
+	depends on IPV6 && EXPERIMENTAL
+	---help---
+	  Experimental support for IPv6 multicast forwarding.
+	  If unsure, say N.
+