net: dsa: ksz: Add STP multicast handling

In case the destination address is link local, add override bit into the
switch tag to let such a packet through the switch even if the port is
blocked.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Cc: Woojung Huh <woojung.huh@microchip.com>
Cc: David S. Miller <davem@davemloft.net>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/tag_ksz.c

@@ -110,6 +110,10 @@ static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
 	addr = skb_mac_header(nskb);
 
 	*tag = BIT(dp->index);
+
+	if (is_link_local_ether_addr(addr))
+		*tag |= KSZ9477_TAIL_TAG_OVERRIDE;
+
 	*tag = cpu_to_be16(*tag);
 
 	return nskb;