tg3: Raise the jumbo frame BD flag threshold

The current transmit routines set the jumbo frame BD flag too
aggressively.  This can reduce performance for common cases.  This patch
raises the jumbo flag threshold to 1518, up from 1500.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Benjamin Li <benli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index afb79db..b8ae5e1 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -5761,7 +5761,7 @@
 	dma_unmap_addr_set(&tnapi->tx_buffers[entry], mapping, mapping);
 
 	if ((tp->tg3_flags3 & TG3_FLG3_USE_JUMBO_BDFLAG) &&
-	    !mss && skb->len > ETH_DATA_LEN)
+	    !mss && skb->len > VLAN_ETH_FRAME_LEN)
 		base_flags |= TXD_FLAG_JMB_PKT;
 
 	tg3_set_txd(tnapi, entry, mapping, len, base_flags,
@@ -5995,7 +5995,7 @@
 #endif
 
 	if ((tp->tg3_flags3 & TG3_FLG3_USE_JUMBO_BDFLAG) &&
-	    !mss && skb->len > ETH_DATA_LEN)
+	    !mss && skb->len > VLAN_ETH_FRAME_LEN)
 		base_flags |= TXD_FLAG_JMB_PKT;
 
 	len = skb_headlen(skb);