e1000e: Disable ASPM L1 on 82574

commit id d4a4206ebbaf48b55803a7eb34e330530d83a889

ASPM on the 82574 causes trouble. Currently the driver disables L0s for
this NIC but only disables L1 if the MTU is >1500. This patch simply
causes L1 to be disabled regardless of the MTU setting.

Signed-off-by: Chris Boot <bootc@bootc.net>
Cc: "Wyborny, Carolyn" <carolyn.wyborny@intel.com>
Cc: Nix <nix@esperi.org.uk>
Link: https://lkml.org/lkml/2012/3/19/362
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
[Jeff Kirsher: Backport to 3.2-3.4 kernels]
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>