tcp: connect() from bound sockets can be faster

__inet_hash_connect() does not use its third argument (port_offset)
if socket was already bound to a source port.

No need to perform useless but expensive md5 computations.

Reported-by: Crestez Dan Leonard <cdleonard@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 1b336dc..5f9b063 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -394,9 +394,10 @@
 	return -EADDRNOTAVAIL;
 }
 
-static inline u32 inet_sk_port_offset(const struct sock *sk)
+static u32 inet_sk_port_offset(const struct sock *sk)
 {
 	const struct inet_sock *inet = inet_sk(sk);
+
 	return secure_ipv4_port_ephemeral(inet->inet_rcv_saddr,
 					  inet->inet_daddr,
 					  inet->inet_dport);
@@ -600,7 +601,11 @@
 int inet_hash_connect(struct inet_timewait_death_row *death_row,
 		      struct sock *sk)
 {
-	return __inet_hash_connect(death_row, sk, inet_sk_port_offset(sk),
+	u32 port_offset = 0;
+
+	if (!inet_sk(sk)->inet_num)
+		port_offset = inet_sk_port_offset(sk);
+	return __inet_hash_connect(death_row, sk, port_offset,
 				   __inet_check_established);
 }
 EXPORT_SYMBOL_GPL(inet_hash_connect);