net: dsa: mv88e6xxx: Add tx fwd offload PVT on intermediate devices

In a typical mv88e6xxx switch tree like this:

  CPU
   |    .----.
.--0--. | .--0--.
| sw0 | | | sw1 |
'-1-2-' | '-1-2-'
    '---'

If sw1p{1,2} are added to a bridge that sw0p1 is not a part of, sw0
still needs to add a crosschip PVT entry for the virtual DSA device
assigned to represent the bridge.

Fixes: ce5df689 ("net: dsa: mv88e6xxx: map virtual bridges with forwarding offload in the PVT")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -2531,6 +2531,7 @@ static int mv88e6xxx_crosschip_bridge_join(struct dsa_switch *ds,
 
 	mv88e6xxx_reg_lock(chip);
 	err = mv88e6xxx_pvt_map(chip, sw_index, port);
+	err = err ? : mv88e6xxx_map_virtual_bridge_to_pvt(ds, bridge.num);
 	mv88e6xxx_reg_unlock(chip);
 
 	return err;
@@ -2546,7 +2547,8 @@ static void mv88e6xxx_crosschip_bridge_leave(struct dsa_switch *ds,
 		return;
 
 	mv88e6xxx_reg_lock(chip);
-	if (mv88e6xxx_pvt_map(chip, sw_index, port))
+	if (mv88e6xxx_pvt_map(chip, sw_index, port) ||
+	    mv88e6xxx_map_virtual_bridge_to_pvt(ds, bridge.num))
 		dev_err(ds->dev, "failed to remap cross-chip Port VLAN\n");
 	mv88e6xxx_reg_unlock(chip);
 }