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 <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/esp4_offload.c b/net/ipv4/esp4_offload.c
index 19bd22a..8756e0e 100644
--- a/net/ipv4/esp4_offload.c
+++ b/net/ipv4/esp4_offload.c
@@ -115,6 +115,7 @@ static struct sk_buff *esp4_gso_segment(struct sk_buff *skb,
 	struct crypto_aead *aead;
 	netdev_features_t esp_features = features;
 	struct xfrm_offload *xo = xfrm_offload(skb);
+	struct sec_path *sp;
 
 	if (!xo)
 		return ERR_PTR(-EINVAL);
@@ -122,7 +123,8 @@ static struct sk_buff *esp4_gso_segment(struct sk_buff *skb,
 	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_ESP))
 		return ERR_PTR(-EINVAL);
 
-	x = skb->sp->xvec[skb->sp->len - 1];
+	sp = skb_sec_path(skb);
+	x = sp->xvec[sp->len - 1];
 	aead = x->data;
 	esph = ip_esp_hdr(skb);