net: Add functions netif_reset_xps_queue and netif_set_xps_queue

This patch adds two functions, netif_reset_xps_queue and
netif_set_xps_queue.  The main idea behind these two functions is to
provide a mechanism through which drivers can update their defaults in
regards to XPS.

Currently no such mechanism exists and as a result we cannot use XPS for
things such as ATR which would require a basic configuration to start in
which the Tx queues are mapped to CPUs via a 1:1 mapping.  With this change
I am making it possible for drivers such as ixgbe to be able to use the XPS
feature by controlling the default configuration.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -2103,6 +2103,19 @@ static inline void netif_wake_subqueue(struct net_device *dev, u16 queue_index)
 		__netif_schedule(txq->qdisc);
 }
 
+#ifdef CONFIG_XPS
+extern void netif_reset_xps_queue(struct net_device *dev, u16 index);
+extern int netif_set_xps_queue(struct net_device *dev, struct cpumask *mask,
+			       u16 index);
+#else
+static inline int netif_set_xps_queue(struct net_device *dev,
+				      struct cpumask *mask,
+				      u16 index)
+{
+	return 0;
+}
+#endif
+
 /*
  * Returns a Tx hash for the given packet when dev->real_num_tx_queues is used
  * as a distribution range limit for the returned value.