i40e: add double of VLAN header when computing the max MTU

commit ce45ffb upstream.

Include the second VLAN HLEN into account when computing the maximum
MTU size as other drivers do.

Fixes: 0c8493d ("i40e: add XDP support for pass and drop actions")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Tested-by: Chandan Kumar Rout <chandanx.rout@intel.com> (A Contingent Worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -2480,7 +2480,7 @@ static int i40e_change_mtu(struct net_device *netdev, int new_mtu)
 	struct i40e_pf *pf = vsi->back;
 
 	if (i40e_enabled_xdp_vsi(vsi)) {
-		int frame_size = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;
+		int frame_size = new_mtu + I40E_PACKET_HDR_PAD;
 
 		if (frame_size > i40e_max_xdp_frame_size(vsi))
 			return -EINVAL;