This patch enables a bit that prevents read DMA overflows and adjusts
the txmbuf margin from the hardware default.  The combination of these
modifications prevents a tx data corruption issue we were seeing on the
5719.
Signed-off-by: NMatt Carlson <mcarlson@broadcom.com>
Reviewed-by: NMichael Chan <mchan@broadcom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>