packet: convert socket list to RCU (v3)

Convert AF_PACKET to use RCU, eliminating one more reader/writer lock.

There is no need for a real sk_del_node_init_rcu(), because sk_del_node_init
is doing the equivalent thing to hlst_del_init_rcu already; but added
some comments to try and make that obvious.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/packet.h b/include/net/netns/packet.h
index 637daf6..cb4e894 100644
--- a/include/net/netns/packet.h
+++ b/include/net/netns/packet.h
@@ -4,11 +4,11 @@
 #ifndef __NETNS_PACKET_H__
 #define __NETNS_PACKET_H__
 
-#include <linux/list.h>
+#include <linux/rculist.h>
 #include <linux/spinlock.h>
 
 struct netns_packet {
-	rwlock_t		sklist_lock;
+	spinlock_t		sklist_lock;
 	struct hlist_head	sklist;
 };