net: dsa: use the ETH_MIN_MTU and ETH_DATA_LEN default values

Now that DSA supports MTU configuration, undo the effects of commit
8b1efc0f83f1 ("net: remove MTU limits on a few ether_setup callers") and
let DSA interfaces use the default min_mtu and max_mtu specified by
ether_setup(). This is more important for min_mtu: since DSA is
Ethernet, the minimum MTU is the same as of any other Ethernet
interface, and definitely not zero. For the max_mtu, we have a callback
through which drivers can override that, if they want to.

Signed-off-by: Vladimir Oltean <[e-mail]>
Reviewed-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/dsa/slave.c

···
 		eth_hw_addr_inherit(slave_dev, master);
 	slave_dev->priv_flags |= IFF_NO_QUEUE;
 	slave_dev->netdev_ops = &dsa_slave_netdev_ops;
-	slave_dev->min_mtu = 0;
 	if (ds->ops->port_max_mtu)
 		slave_dev->max_mtu = ds->ops->port_max_mtu(ds, port->index);
-	else
-		slave_dev->max_mtu = ETH_MAX_MTU;
 	SET_NETDEV_DEVTYPE(slave_dev, &dsa_type);
 
 	netdev_for_each_tx_queue(slave_dev, dsa_slave_set_lockdep_class_one,