sock: Introduce named constants for sk_reuse

Name them in a "backward compatible" manner, i.e. reuse or not
are still 1 and 0 respectively. The reuse value of 2 means that
the socket with it will forcibly reuse everyone else's port.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/tcp_listen.c

@@ -145,7 +145,7 @@ int rds_tcp_listen_init(void)
 	if (ret < 0)
 		goto out;
 
-	sock->sk->sk_reuse = 1;
+	sock->sk->sk_reuse = SK_CAN_REUSE;
 	rds_tcp_nonagle(sock);
 
 	write_lock_bh(&sock->sk->sk_callback_lock);