net: dsa: print the MTU value that could not be set

These warnings become somewhat more informative when they include the
MTU value that could not be set and not just the errno.

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Link: https://lore.kernel.org/r/20201205133944.10182-1-rasmus.villemoes@prevas.dk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/master.c

@@ -308,14 +308,15 @@ static struct lock_class_key dsa_master_addr_list_lock_key;
 
 int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
 {
+	int mtu = ETH_DATA_LEN + cpu_dp->tag_ops->overhead;
 	int ret;
 
 	rtnl_lock();
-	ret = dev_set_mtu(dev, ETH_DATA_LEN + cpu_dp->tag_ops->overhead);
+	ret = dev_set_mtu(dev, mtu);
 	rtnl_unlock();
 	if (ret)
-		netdev_warn(dev, "error %d setting MTU to include DSA overhead\n",
+		netdev_warn(dev, "error %d setting MTU to %d to include DSA overhead\n",
-			    ret);
+			    ret, mtu);
 
 	/* If we use a tagging format that doesn't have an ethertype
 	 * field, make sure that all packets from this point on get

net/dsa/slave.c

@@ -1850,8 +1850,8 @@ int dsa_slave_create(struct dsa_port *port)
 	ret = dsa_slave_change_mtu(slave_dev, ETH_DATA_LEN);
 	rtnl_unlock();
 	if (ret && ret != -EOPNOTSUPP)
-		dev_warn(ds->dev, "nonfatal error %d setting MTU on port %d\n",
+		dev_warn(ds->dev, "nonfatal error %d setting MTU to %d on port %d\n",
-			 ret, port->index);
+			 ret, ETH_DATA_LEN, port->index);
 
 	netif_carrier_off(slave_dev);