[NETNS]: Compilation fix for include/linux/netdevice.h.

Commit commit c346dca1
([NET] NETNS: Omit net_device->nd_net without CONFIG_NET_NS)
breaks compilation with CONFIG_NET_NS set.

Fix the typo.
Signed-off-by: NDenis V. Lunev <den@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -756,7 +756,7 @@ static inline
 void dev_net_set(struct net_device *dev, const struct net *net)
 {
 #ifdef CONFIG_NET_NS
-	dev->nd_dev = net;
+	dev->nd_net = net;
 #endif
 }