net: dsa: lan9303: lan9303_rcv set skb->offload_fwd_mark

The chip flood broadcast and unknown multicast frames.
On receive set skb->offload_fwd_mark to prevent the SW from flooding to the
same ports.

One exception: Because the ALR is set up to forward STP BPDUs only to CPU,
the SW bridge should flood STP BPDUs if local STP is not enabled.
This is archived by not setting skb->offload_fwd_mark on STP BPDUs.
Signed-off-by: Egil Hjelmeland <privat@egil-hjelmeland.no>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_lan9303.c

@@ -126,6 +126,8 @@ static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev,
 	skb_pull_rcsum(skb, 2 + 2);
 	memmove(skb->data - ETH_HLEN, skb->data - (ETH_HLEN + LAN9303_TAG_LEN),
 		2 * ETH_ALEN);
+	skb->offload_fwd_mark = !ether_addr_equal(skb->data - ETH_HLEN,
+						  eth_stp_addr);
 
 	return skb;
 }