net: dsa: mv88e6xxx: override existent unicast portvec in port_fdb_add

Having multiple destination ports for a unicast address does not make
sense.
Make port_db_load_purge override existent unicast portvec instead of
adding a new port bit.

Fixes: 8847293 ("net: dsa: mv88e6xxx: handle multiple ports in ATU")
Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20210130134334.10243-1-dqfext@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -1676,7 +1676,11 @@ static int mv88e6xxx_port_db_load_purge(struct mv88e6xxx_chip *chip, int port,
 		if (!entry.portvec)
 			entry.state = 0;
 	} else {
-		entry.portvec |= BIT(port);
+		if (state == MV88E6XXX_G1_ATU_DATA_STATE_UC_STATIC)
+			entry.portvec = BIT(port);
+		else
+			entry.portvec |= BIT(port);
+
 		entry.state = state;
 	}