tcp: Fix dst leak in tcp_v6_connect().

If a socket is bound to a wildcard address, tcp_v[46]_connect()
updates it with a non-wildcard address based on the route lookup.

After bhash2 was introduced in the cited commit, we must call
inet_bhash2_update_saddr() to update the bhash2 entry as well.

If inet_bhash2_update_saddr() fails, we must release the refcount
for dst by ip_route_connect() or ip6_dst_lookup_flow().

While tcp_v4_connect() calls ip_rt_put() in the error path,
tcp_v6_connect() does not call dst_release().

Let's call dst_release() when inet_bhash2_update_saddr() fails
in tcp_v6_connect().

Fixes: 28044fc ("net: Add a bhash2 table hashed by port and address")
Reported-by: Damiano Melotti <melotti@google.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260506070443.1699879-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: q2ven

net/ipv6/tcp_ipv6.c

@@ -288,8 +288,10 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr_unsized *uaddr,
 		saddr = &fl6->saddr;
 
 		err = inet_bhash2_update_saddr(sk, saddr, AF_INET6);
-		if (err)
+		if (err) {
+			dst_release(dst);
 			goto failure;
+		}
 	}
 
 	/* set the source address */