e1000: add mmiowb() for IA64 to sync tail writes

IA64 SMP systems were seeing TX issues with multiple cpu's attempting
to write tail registers unordered. This mmiowb() fixes the issue.
Signed-off-by: NAuke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: NJesse Brandeburg <jesse.brandeburg@intel.com>

drivers/net/e1000/e1000_main.c

@@ -2867,6 +2867,9 @@ e1000_tx_queue(struct e1000_adapter *adapter, struct e1000_tx_ring *tx_ring,
 
 	tx_ring->next_to_use = i;
 	writel(i, adapter->hw.hw_addr + tx_ring->tdt);
+	/* we need this if more than one processor can write to our tail
+	 * at a time, it syncronizes IO on IA64/Altix systems */
+	mmiowb();
 }
 
 /**