net: dsa: tag_ocelot_8021q: fix inability to inject STP BPDUs into BLOCKING ports

When setting up a bridge with stp_state 1, topology changes are not
detected and loops are not blocked. This is because the standard way of
transmitting a packet, based on VLAN IDs redirected by VCAP IS2 to the
right egress port, does not override the port STP state (in the case of
Ocelot switches, that's really the PGID_SRC masks).

To force a packet to be injected into a port that's BLOCKING, we must
send it as a control packet, which means in the case of this tagger to
send it using the manual register injection method. We already do this
for PTP frames, extend the logic to apply to any link-local MAC DA.

Fixes: 7c83a7c5 ("net: dsa: add a second tagger for Ocelot switches based on tag_8021q")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/tag_ocelot_8021q.c

@@ -42,8 +42,9 @@ static struct sk_buff *ocelot_xmit(struct sk_buff *skb,
 	u16 tx_vid = dsa_8021q_tx_vid(dp->ds, dp->index);
 	u16 queue_mapping = skb_get_queue_mapping(skb);
 	u8 pcp = netdev_txq_to_tc(netdev, queue_mapping);
+	struct ethhdr *hdr = eth_hdr(skb);
 
-	if (ocelot_ptp_rew_op(skb))
+	if (ocelot_ptp_rew_op(skb) || is_link_local_ether_addr(hdr->h_dest))
 		return ocelot_defer_xmit(dp, skb);
 
 	return dsa_8021q_xmit(skb, netdev, ETH_P_8021Q,