e1000e: disable jumbo frames on 82579 when MACsec enabled in EEPROM

If/when an OEM enables MACsec in the 82579 EEPROM, disable jumbo frames
support in the driver due to an interoperability issue in hardware that
prevents jumbo packets from being transmitted or received.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>