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

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

commit 24cd1473c152483f1a181961c5679b5acaf55ec8 upstream.

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

Fixes: 30067ecaebfe ("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>