sit: use dev_sw_netstats_rx_add()

We have a convenient helper, let's use it.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/sit.c

@@ -686,8 +686,6 @@ static int ipip6_rcv(struct sk_buff *skb)
 	tunnel = ipip6_tunnel_lookup(dev_net(skb->dev), skb->dev,
 				     iph->saddr, iph->daddr, sifindex);
 	if (tunnel) {
-		struct pcpu_sw_netstats *tstats;
-
 		if (tunnel->parms.iph.protocol != IPPROTO_IPV6 &&
 		    tunnel->parms.iph.protocol != 0)
 			goto out;
@@ -724,11 +722,7 @@ static int ipip6_rcv(struct sk_buff *skb)
 			}
 		}
 
-		tstats = this_cpu_ptr(tunnel->dev->tstats);
-		u64_stats_update_begin(&tstats->syncp);
-		tstats->rx_packets++;
-		tstats->rx_bytes += skb->len;
-		u64_stats_update_end(&tstats->syncp);
+		dev_sw_netstats_rx_add(tunnel->dev, skb->len);
 
 		netif_rx(skb);