inet: remove rcu protection on tw_net

commit b099ce2602d806 (net: Batch inet_twsk_purge) added rcu protection
on tw_net for no obvious reason.

struct net are refcounted anyway since timewait sockets escape from rcu
protected sections. tw_net stay valid for the whole timwait lifetime.

This also removes a lot of sparse errors.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_timewait_sock.h

@@ -218,20 +218,12 @@ extern void inet_twsk_purge(struct inet_hashinfo *hashinfo,
 static inline
 struct net *twsk_net(const struct inet_timewait_sock *twsk)
 {
-#ifdef CONFIG_NET_NS
-	return rcu_dereference_raw(twsk->tw_net); /* protected by locking, */
-						  /* reference counting, */
-						  /* initialization, or RCU. */
-#else
-	return &init_net;
-#endif
+	return read_pnet(&twsk->tw_net);
 }
 
 static inline
 void twsk_net_set(struct inet_timewait_sock *twsk, struct net *net)
 {
-#ifdef CONFIG_NET_NS
-	rcu_assign_pointer(twsk->tw_net, net);
-#endif
+	write_pnet(&twsk->tw_net, net);
 }
 #endif	/* _INET_TIMEWAIT_SOCK_ */