vrf: Increment Icmp6InMsgs on the original netdev

Get the ingress interface and increment ICMP counters based on that
instead of skb->dev when the the dev is a VRF device.

This is a follow up on the following message:
https://www.spinics.net/lists/netdev/msg560268.html

v2: Avoid changing skb->dev since it has unintended effect for local
    delivery (David Ahern).
Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index bafdd04..375b4b4 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -393,23 +393,28 @@ static struct dst_entry *icmpv6_route_lookup(struct net *net,
 	return ERR_PTR(err);
 }
 
-static int icmp6_iif(const struct sk_buff *skb)
+static struct net_device *icmp6_dev(const struct sk_buff *skb)
 {
-	int iif = skb->dev->ifindex;
+	struct net_device *dev = skb->dev;
 
 	/* for local traffic to local address, skb dev is the loopback
 	 * device. Check if there is a dst attached to the skb and if so
 	 * get the real device index. Same is needed for replies to a link
 	 * local address on a device enslaved to an L3 master device
 	 */
-	if (unlikely(iif == LOOPBACK_IFINDEX || netif_is_l3_master(skb->dev))) {
+	if (unlikely(dev->ifindex == LOOPBACK_IFINDEX || netif_is_l3_master(skb->dev))) {
 		const struct rt6_info *rt6 = skb_rt6_info(skb);
 
 		if (rt6)
-			iif = rt6->rt6i_idev->dev->ifindex;
+			dev = rt6->rt6i_idev->dev;
 	}
 
-	return iif;
+	return dev;
+}
+
+static int icmp6_iif(const struct sk_buff *skb)
+{
+	return icmp6_dev(skb)->ifindex;
 }
 
 /*
@@ -810,7 +815,7 @@ void icmpv6_notify(struct sk_buff *skb, u8 type, u8 code, __be32 info)
 static int icmpv6_rcv(struct sk_buff *skb)
 {
 	struct net *net = dev_net(skb->dev);
-	struct net_device *dev = skb->dev;
+	struct net_device *dev = icmp6_dev(skb);
 	struct inet6_dev *idev = __in6_dev_get(dev);
 	const struct in6_addr *saddr, *daddr;
 	struct icmp6hdr *hdr;