tcp/dccp: avoid one atomic operation for timewait hashdance

First, rename __inet_twsk_hashdance() to inet_twsk_hashdance()

Then, remove one inet_twsk_put() by setting tw_refcnt to 3 instead
of 4, but adding a fat warning that we do not have the right to access
tw anymore after inet_twsk_hashdance()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dccp/minisocks.c

@@ -63,9 +63,10 @@ void dccp_time_wait(struct sock *sk, int state, int timeo)
 		 */
 		local_bh_disable();
 		inet_twsk_schedule(tw, timeo);
-		/* Linkage updates. */
-		__inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
-		inet_twsk_put(tw);
+		/* Linkage updates.
+		 * Note that access to tw after this point is illegal.
+		 */
+		inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
 		local_bh_enable();
 	} else {
 		/* Sorry, if we're out of memory, just CLOSE this