loggen: close connections correctly (4-way termination)

This is important especially when TLS 1.3 is used.

> TLSv1.3 sessions are not established during the main handshake.
> Instead, after the main handshake is complete, a server may send some
> NewSessionTicket messages to the client.

If a client sends messages and then closes the connection immediately
without reading any NewSessionTickets from the server, the server may
not read the messages that were already sent by the client.

This issue has been fixed in openssl/openssl#6944,
but a full TCP shutdown is still required to make the server read the data.

Also: openssl/openssl#6904

Backported from OSE: da03117a89aab7158d9a6db4d275d0358a71323c

Signed-off-by: László Várady <laszlo.varady@protonmail.com>
Signed-off-by: Attila Szakacs <attila.szakacs@oneidentity.com>

tests/loggen/loggen.c

@@ -821,6 +821,7 @@ idle_thread(gpointer st)
   while (!threads_stop)
     g_cond_wait(thread_cond, thread_lock);
   g_mutex_unlock(thread_lock);
+  shutdown(sock, SHUT_RDWR);
   close(sock);
   return NULL;
 error:
@@ -1032,6 +1033,7 @@ active_thread(gpointer st)
   if (active_finished == active_connections)
     g_cond_signal(thread_finished);
   g_mutex_unlock(thread_lock);
+  shutdown(sock, SHUT_RDWR);
   close(sock);
   if (readfrom && readfrom != stdin)
     fclose(readfrom);