ip: Router Alert RCU conversion

Straightforward conversion to RCU.

One rwlock becomes a spinlock, and is static.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip.h b/include/net/ip.h
index 452f229..9982c97 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -62,10 +62,10 @@
 	struct ip_ra_chain	*next;
 	struct sock		*sk;
 	void			(*destructor)(struct sock *);
+	struct rcu_head		rcu;
 };
 
 extern struct ip_ra_chain *ip_ra_chain;
-extern rwlock_t ip_ra_lock;
 
 /* IP flags. */
 #define IP_CE		0x8000		/* Flag: "Congestion"		*/