ip6_tunnel: allow not to count pkts on tstats by passing dev as NULL

A similar fix to Patch "ip_tunnel: allow not to count pkts on tstats by
setting skb's dev to NULL" is also needed by ip6_tunnel.
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_tunnel.h

@@ -158,9 +158,12 @@ static inline void ip6tunnel_xmit(struct sock *sk, struct sk_buff *skb,
 	memset(skb->cb, 0, sizeof(struct inet6_skb_parm));
 	pkt_len = skb->len - skb_inner_network_offset(skb);
 	err = ip6_local_out(dev_net(skb_dst(skb)->dev), sk, skb);
-	if (unlikely(net_xmit_eval(err)))
-		pkt_len = -1;
-	iptunnel_xmit_stats(dev, pkt_len);
+
+	if (dev) {
+		if (unlikely(net_xmit_eval(err)))
+			pkt_len = -1;
+		iptunnel_xmit_stats(dev, pkt_len);
+	}
 }
 #endif
 #endif