[INET_TWSK]: Introduce inet_twsk_alloc

With the parts of tcp_time_wait that are not TCP specific, tcp_time_wait uses
it and so will dccp_time_wait.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_timewait_sock.h

@@ -142,6 +142,9 @@ static inline void inet_twsk_put(struct inet_timewait_sock *tw)
 	}
 }
 
+extern struct inet_timewait_sock *inet_twsk_alloc(const struct sock *sk,
+						  const int state);
+
 extern void __inet_twsk_kill(struct inet_timewait_sock *tw,
 			     struct inet_hashinfo *hashinfo);