igb: igb should not flag lltx

Igb has flags enabling lltx but this is a holdover from the earlier
e1000 driver which the igb driver was based off of.

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>