net: use skb_sec_path helper in more places

skb_sec_path gains 'const' qualifier to avoid
xt_policy.c: 'skb_sec_path' discards 'const' qualifier from pointer target type

same reasoning as previous conversions: Won't need to touch these
spots anymore when skb->sp is removed.

Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
diff --git a/net/ipv6/xfrm6_input.c b/net/ipv6/xfrm6_input.c
index 97c69df..a52cb3f 100644
--- a/net/ipv6/xfrm6_input.c
+++ b/net/ipv6/xfrm6_input.c
@@ -147,7 +147,7 @@ int xfrm6_input_addr(struct sk_buff *skb, xfrm_address_t *daddr,
 		goto drop;
 	}
 
-	skb->sp->xvec[skb->sp->len++] = x;
+	sp->xvec[sp->len++] = x;
 
 	spin_lock(&x->lock);