igb: restrict WoL for 82576 ET2 Quad Port Server Adapter

Restrict Wake-on-LAN to first port on 82576 ET2 quad port NICs, as it is
only supported there.

Signed-off-by: Stefan Assmann <sassmann@redhat.com>
Acked-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>