tcp: use tcp_md5_needed for timewait sockets

This might speedup tcp_twsk_destructor() a bit,
avoiding a cache line miss.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_minisocks.c

@@ -294,13 +294,16 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
 		 * so the timewait ack generating code has the key.
 		 */
 		do {
-			struct tcp_md5sig_key *key;
 			tcptw->tw_md5_key = NULL;
+			if (static_branch_unlikely(&tcp_md5_needed)) {
+				struct tcp_md5sig_key *key;
+
 				key = tp->af_specific->md5_lookup(sk, sk);
 				if (key) {
 					tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
 					BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
 				}
+			}
 		} while (0);
 #endif
 
@@ -338,10 +341,12 @@ EXPORT_SYMBOL(tcp_time_wait);
 void tcp_twsk_destructor(struct sock *sk)
 {
 #ifdef CONFIG_TCP_MD5SIG
+	if (static_branch_unlikely(&tcp_md5_needed)) {
 		struct tcp_timewait_sock *twsk = tcp_twsk(sk);
 
 		if (twsk->tw_md5_key)
 			kfree_rcu(twsk->tw_md5_key, rcu);
+	}
 #endif
 }
 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);