e1000e: workaround hw errata

There is a hardware errata in some revisions of the 82574 that needs
to be worked around in the driver by setting a register bit at init.

If this bit is not set A0 versions of the 82574 can generate
tx hangs.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>