timewait_sock: Create and use getpeer op.

The only thing AF-specific about remembering the timestamp
for a time-wait TCP socket is getting the peer.

Abstract that behind a new timewait_sock_ops vector.

Support for real IPV6 sockets is not filled in yet, but
curiously this makes timewait recycling start to work
for v4-mapped ipv6 sockets.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/timewait_sock.h b/include/net/timewait_sock.h
index 97c3b14..053b3cf 100644
--- a/include/net/timewait_sock.h
+++ b/include/net/timewait_sock.h
@@ -21,6 +21,7 @@
 	int		(*twsk_unique)(struct sock *sk,
 				       struct sock *sktw, void *twp);
 	void		(*twsk_destructor)(struct sock *sk);
+	void		*(*twsk_getpeer)(struct sock *sk);
 };
 
 static inline int twsk_unique(struct sock *sk, struct sock *sktw, void *twp)
@@ -39,4 +40,11 @@
 		sk->sk_prot->twsk_prot->twsk_destructor(sk);
 }
 
+static inline void *twsk_getpeer(struct sock *sk)
+{
+	if (sk->sk_prot->twsk_prot->twsk_getpeer)
+		return sk->sk_prot->twsk_prot->twsk_getpeer(sk);
+	return NULL;
+}
+
 #endif /* _TIMEWAIT_SOCK_H */