ixgbe: Enable Jumbo Frames on the X540 10Gigabit Controller

The X540 controller supports jumbo frames in SR-IOV mode.  Allow
configuration of jumbo frames either in the PF driver or on behalf of
a VF.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>