ipv4: use skb frags api in udp4_hwcsum()

Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -727,13 +727,12 @@ EXPORT_SYMBOL(udp_flush_pending_frames);
 void udp4_hwcsum(struct sk_buff *skb, __be32 src, __be32 dst)
 {
 	struct udphdr *uh = udp_hdr(skb);
-	struct sk_buff *frags = skb_shinfo(skb)->frag_list;
 	int offset = skb_transport_offset(skb);
 	int len = skb->len - offset;
 	int hlen = len;
 	__wsum csum = 0;
 
-	if (!frags) {
+	if (!skb_has_frag_list(skb)) {
 		/*
 		 * Only one fragment on the socket.
 		 */
@@ -742,15 +741,17 @@ void udp4_hwcsum(struct sk_buff *skb, __be32 src, __be32 dst)
 		uh->check = ~csum_tcpudp_magic(src, dst, len,
 					       IPPROTO_UDP, 0);
 	} else {
+		struct sk_buff *frags;
+
 		/*
 		 * HW-checksum won't work as there are two or more
 		 * fragments on the socket so that all csums of sk_buffs
 		 * should be together
 		 */
-		do {
+		skb_walk_frags(skb, frags) {
 			csum = csum_add(csum, frags->csum);
 			hlen -= frags->len;
-		} while ((frags = frags->next));
+		}
 
 		csum = skb_checksum(skb, offset, hlen, csum);
 		skb->ip_summed = CHECKSUM_NONE;