[IPV6] ROUTE: Put SUBTREE() as FIB6_SUBTREE() into ip6_fib.h for future use.

Based on MIPL2 kernel patch.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Ville Nuorvala <vnuorval@tcs.hut.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 9610b887f..6a3f26a 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -60,6 +60,11 @@
 	__u32			fn_sernum;
 };
 
+#ifndef CONFIG_IPV6_SUBTREES
+#define FIB6_SUBTREE(fn)	NULL
+#else
+#define FIB6_SUBTREE(fn)	((fn)->subtree)
+#endif
 
 /*
  *	routing information