igb: Fix DCA errors and do not use context index for 82576

82576 was being incorrectly flagged as needing a context index.  It does not as
each ring has it's own table of 2 contexts.

Driver was registering after registering the driver instead of the other way around.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>