net: reduce structures when XFRM=n

ifdef out
* struct sk_buff::sp		(pointer)
* struct dst_entry::xfrm	(pointer)
* struct sock::sk_policy	(2 pointers)

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/dst.h b/include/net/dst.h
index 8a8b71e..f96c4ba 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -59,8 +59,9 @@
 
 	struct neighbour	*neighbour;
 	struct hh_cache		*hh;
+#ifdef CONFIG_XFRM
 	struct xfrm_state	*xfrm;
-
+#endif
 	int			(*input)(struct sk_buff*);
 	int			(*output)(struct sk_buff*);