[IPV6] KCONFIG: Add subtrees support.

This is for developers only.
Based on MIPL2 kernel patch.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Ville Nuorvala <vnuorval@tcs.hut.fi
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/Kconfig

@@ -136,6 +136,20 @@ config IPV6_TUNNEL
 
 	  If unsure, say N.
 
+config IPV6_SUBTREES
+	bool "IPv6: source address based routing"
+	depends on IPV6 && EXPERIMENTAL
+	---help---
+	  Enable routing by source address or prefix.
+
+	  The destination address is still the primary routing key, so mixing
+	  normal and source prefix specific routes in the same routing table
+	  may sometimes lead to unintended routing behavior.  This can be
+	  avoided by defining different routing tables for the normal and
+	  source prefix specific routes.
+
+	  If unsure, say N.
+
 config IPV6_MULTIPLE_TABLES
 	bool "IPv6: Multiple Routing Tables"
 	depends on IPV6 && EXPERIMENTAL