tg3: Use tg3_start_xmit_dma_bug for 5717 A0

The A0 revision of the 5717 has problems with short packet fragments.
It needs to use the tg3_start_xmit_dma_bug() routine.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>