igb: Fix register defines for all non-82575 hardware

It looks like the register defines for DCA were never updated after going from
82575 to 82576.  This change addresses that by updating the defines.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>