e1000: FIX: Stop raw interrupts disabled nag from RT

Current e1000_xmit_frame spews raw interrupt disabled nag messages when
used with RT kernel patches.  This patch uses spin_trylock_irqsave,
which allows RT patches to properly manage the irq semantics.
Signed-off-by: NMark Huth <mhuth@mvista.com>
Signed-off-by: NAuke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/net/e1000/e1000_main.c

@@ -3378,12 +3378,9 @@ e1000_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
 	    (adapter->hw.mac_type == e1000_82573))
 		e1000_transfer_dhcp_info(adapter, skb);
 
-	local_irq_save(flags);
-	if (!spin_trylock(&tx_ring->tx_lock)) {
+	if (!spin_trylock_irqsave(&tx_ring->tx_lock, flags))
 		/* Collision - tell upper layer to requeue */
-		local_irq_restore(flags);
 		return NETDEV_TX_LOCKED;
-	}
 
 	/* need: count + 2 desc gap to keep tail from touching
 	 * head, otherwise try next time */