tg3: Fix 5906 transmit hangs

The 5906 has trouble with fragments that are less than 8 bytes in size.
This patch works around the problem by pivoting the 5906's transmit
routine to tg3_start_xmit_dma_bug() and introducing a new SHORT_DMA_BUG
flag that enables code to detect and react to the problematic condition.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tg3.h b/drivers/net/tg3.h
index b603810..a5568a1 100644
--- a/drivers/net/tg3.h
+++ b/drivers/net/tg3.h
@@ -2761,6 +2761,7 @@
 #define TG3_FLG3_ENABLE_RSS		0x00020000
 #define TG3_FLG3_4G_DMA_BNDRY_BUG	0x00080000
 #define TG3_FLG3_40BIT_DMA_LIMIT_BUG	0x00100000
+#define TG3_FLG3_SHORT_DMA_BUG		0x00200000
 
 	struct timer_list		timer;
 	u16				timer_counter;