net: dsa: lan9303: Clear offload_fwd_mark for IGMP

Now that IGMP packets no longer is flooded in HW, we want the SW bridge to
forward packets based on bridge configuration. To make that happen,
IGMP packets must have skb->offload_fwd_mark = 0.
Signed-off-by: Egil Hjelmeland <privat@egil-hjelmeland.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_lan9303.c

@@ -92,6 +92,8 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
 {
 	u16 *lan9303_tag;
 	unsigned int source_port;
+	u16 ether_type_nw;
+	u8 ip_protocol;
 
 	if (unlikely(!pskb_may_pull(skb, LAN9303_TAG_LEN))) {
 		dev_warn_ratelimited(&dev->dev,
@@ -129,6 +131,17 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
 	skb->offload_fwd_mark = !ether_addr_equal(skb->data - ETH_HLEN,
 						  eth_stp_addr);
 
+	/* We also need IGMP packets to have skb->offload_fwd_mark = 0.
+	 * Solving this for all conceivable situations would add more cost to
+	 * every packet. Instead we handle just the common case:
+	 * No VLAN tag + Ethernet II framing.
+	 * Test least probable term first.
+	 */
+	ether_type_nw = lan9303_tag[2];
+	ip_protocol = *(skb->data + 9);
+	if (ip_protocol == IPPROTO_IGMP && ether_type_nw == htons(ETH_P_IP))
+		skb->offload_fwd_mark = 0;
+
 	return skb;
 }