[3/6] vxge: improve tx performance by using mmiowb() instead of wmb()

wmb() is extremely heavy on x86.  The semantics required in the driver are 
provided by mmiowb(), so use that and improve tx performance on P4 Xeons by 
5-10%.

Signed-off-by: Benjamin LaHaise <redacted>
Signed-off-by: Sreenivasa Honnur <redacted>
Signed-off-by: Ramkrishna Vepa <redacted>
---

diff --git a/drivers/net/vxge/vxge-traffic.c b/drivers/net/vxge/vxge-traffic.c
index 370f55c..0efb769 100644
--- a/drivers/net/vxge/vxge-traffic.c
+++ b/drivers/net/vxge/vxge-traffic.c

@@ -1070,11 +1070,11 @@ static void __vxge_hw_non_offload_db_post(struct __vxge_hw_fifo *fifo,
 		VXGE_HW_NODBW_GET_NO_SNOOP(no_snoop),
 		&fifo->nofl_db->control_0);
 
-	wmb();
+	mmiowb();
 
 	writeq(txdl_ptr, &fifo->nofl_db->txdl_ptr);
-	wmb();
 
+	mmiowb();
 }
 
 /**