[IPV6]: Make fib6_node subtree depend on IPV6_SUBTREES

Make fib6_node 'subtree' depend on IPV6_SUBTREES.

Signed-off-by: Kim Nordlund <kim.nordlund@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index f9cde44..7be4f4e 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -50,9 +50,9 @@
 	struct fib6_node	*parent;
 	struct fib6_node	*left;
 	struct fib6_node	*right;
-
+#ifdef CONFIG_IPV6_SUBTREES
 	struct fib6_node	*subtree;
-
+#endif
 	struct rt6_info		*leaf;
 
 	__u16			fn_bit;		/* bit key */