i40e: clamp jumbo frame size

The driver was allowing the user to set larger size MTU
than the hardware was being configured to support.

The driver was already using VLAN_HLEN when setting the
hardware max receivable frame size, so just add it to the
netdev MTU set entry point as well.

Change-ID: Ie20e2a35d04f8c411253e255bea79ca69aaeaea3
Signed-off-by: NJesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -1698,7 +1698,7 @@ static void i40e_sync_filters_subtask(struct i40e_pf *pf)
 static int i40e_change_mtu(struct net_device *netdev, int new_mtu)
 {
 	struct i40e_netdev_priv *np = netdev_priv(netdev);
-	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
+	int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;
 	struct i40e_vsi *vsi = np->vsi;
 
 	/* MTU < 68 is an error and causes problems on some kernels */