xfrm: Mark flowi arg to ->fill_dst() const.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index f8ccb97..fa0b7f3 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1369,7 +1369,7 @@
 }
 
 static inline int xfrm_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
-				struct flowi *fl)
+				const struct flowi *fl)
 {
 	struct xfrm_policy_afinfo *afinfo =
 		xfrm_policy_get_afinfo(xdst->u.dst.ops->family);