mac80211: support use of NAPI for bottom-half processing

This patch implement basic infrastructure to support use of NAPI by
mac80211-based hardware drivers.

Because mac80211 devices can support multiple netdevs, a dummy netdev
is used for interfacing with the NAPI code in the core of the network
stack.  That structure is hidden from the hardware drivers, but the
actual napi_struct is exposed in the ieee80211_hw structure so that the
poll routines in drivers can retrieve that structure.  Hardware drivers
can also specify their own weight value for NAPI polling.

Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/ieee80211_i.h

@@ -870,6 +870,11 @@ struct ieee80211_local {
 		struct dentry *keys;
 	} debugfs;
 #endif
+
+	/* dummy netdev for use w/ NAPI */
+	struct net_device napi_dev;
+
+	struct napi_struct napi;
 };
 
 static inline struct ieee80211_sub_if_data *