e1000e: 82574/82583 Tx hang workaround

On 82574/82583, there is a hardware bug which might cause a Tx hang when
the internal buffer is full.  Setting this bit enables a hardware fix to
work around the issue.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>