ethernet/atheros: use core min/max MTU checking

atl2: min_mtu 40, max_mtu 1504

- Remove a few redundant defines that already have equivalents in
  if_ether.h.

atl1: min_mtu 42, max_mtu 10218

atl1e: min_mtu 42, max_mtu 8170

atl1c: min_mtu 42, max_mtu 6122/1500

- GbE hardware gets a max_mtu of 6122, slower hardware gets 1500.

alx: min_mtu 34, max_mtu 9256

- Not so sure that minimum MTU number is really what was intended, but
  that's what the math actually makes it out to be, due to max_frame
  manipulations and comparison in alx_change_mtu, rather than just
  comparing new_mtu. (I think 68 was the intended min_mtu value).

CC: netdev@vger.kernel.org
CC: Jay Cliburn <jcliburn@gmail.com>
CC: Chris Snook <chris.snook@gmail.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/atl1e/atl1e_main.c

@@ -439,16 +439,10 @@ static int atl1e_set_features(struct net_device *netdev,
 static int atl1e_change_mtu(struct net_device *netdev, int new_mtu)
 {
 	struct atl1e_adapter *adapter = netdev_priv(netdev);
-	int old_mtu   = netdev->mtu;
 	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;
 
-	if ((max_frame < ETH_ZLEN + ETH_FCS_LEN) ||
-			(max_frame > MAX_JUMBO_FRAME_SIZE)) {
-		netdev_warn(adapter->netdev, "invalid MTU setting\n");
-		return -EINVAL;
-	}
 	/* set MTU */
-	if (old_mtu != new_mtu && netif_running(netdev)) {
+	if (netif_running(netdev)) {
 		while (test_and_set_bit(__AT_RESETTING, &adapter->flags))
 			msleep(1);
 		netdev->mtu = new_mtu;
@@ -2272,6 +2266,10 @@ static int atl1e_init_netdev(struct net_device *netdev, struct pci_dev *pdev)
 	netdev->netdev_ops = &atl1e_netdev_ops;
 
 	netdev->watchdog_timeo = AT_TX_WATCHDOG;
+	/* MTU range: 42 - 8170 */
+	netdev->min_mtu = ETH_ZLEN - (ETH_HLEN + VLAN_HLEN);
+	netdev->max_mtu = MAX_JUMBO_FRAME_SIZE -
+			  (ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN);
 	atl1e_set_ethtool_ops(netdev);
 
 	netdev->hw_features = NETIF_F_SG | NETIF_F_HW_CSUM | NETIF_F_TSO |