net: dsa: prepare 'dsa_tag_8021q_bridge_join' for standalone use

The 'dsa_tag_8021q_bridge_join' could be used as a generic implementation
of the 'ds->ops->port_bridge_join()' function. However, it is necessary
to synchronize their arguments.

This patch also moves the 'tx_fwd_offload' flag configuration line into
'dsa_tag_8021q_bridge_join' body. Currently, every (sja1105) driver sets
it, and the future vsc73xx implementation will also need it for
simplification.

Suggested-by: Vladimir Oltean <[e-mail]>
Signed-off-by: Pawel Dembicki <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/dsa/sja1105/sja1105_main.c

···
 	if (rc)
 		return rc;
 
-	rc = dsa_tag_8021q_bridge_join(ds, port, bridge);
+	rc = dsa_tag_8021q_bridge_join(ds, port, bridge, tx_fwd_offload,
+				       extack);
 	if (rc) {
 		sja1105_bridge_member(ds, port, bridge, false);
 		return rc;
 	}
-
-	*tx_fwd_offload = true;
 
 	return 0;
 }

include/linux/dsa/8021q.h

···
 void dsa_tag_8021q_unregister(struct dsa_switch *ds);
 
 int dsa_tag_8021q_bridge_join(struct dsa_switch *ds, int port,
-			      struct dsa_bridge bridge);
+			      struct dsa_bridge bridge, bool *tx_fwd_offload,
+			      struct netlink_ext_ack *extack);
 
 void dsa_tag_8021q_bridge_leave(struct dsa_switch *ds, int port,
 				struct dsa_bridge bridge);

net/dsa/tag_8021q.c

···
  * be used for VLAN-unaware bridging.
  */
 int dsa_tag_8021q_bridge_join(struct dsa_switch *ds, int port,
-			      struct dsa_bridge bridge)
+			      struct dsa_bridge bridge, bool *tx_fwd_offload,
+			      struct netlink_ext_ack *extack)
 {
 	struct dsa_port *dp = dsa_to_port(ds, port);
 	u16 standalone_vid, bridge_vid;
···
 		return err;
 
 	dsa_port_tag_8021q_vlan_del(dp, standalone_vid, false);
+
+	*tx_fwd_offload = true;
 
 	return 0;
 }