cgrates: fix infinite re-connect issue

When a non-default connection would have reconnected, due to a
mishandling of the return code of the `cgrc_reconn` function, a new
connection would have been created every time, resulting in infinite
re-connections. And in time, this would acquire all the available ports
(65k) and would no longer accept new connections.

Many thanks go to Vasilios Tzanoudakis (@vtzan on GitHub) for reporting
and providing a solid testbed for this.
Close #2850

modules/cgrates/cgrates_engine.c

@@ -34,9 +34,10 @@ static void cgrc_reconn_rpc(int sender, void *p);
 
 static int cgrc_reconn(struct cgr_conn *c)
 {
-	if (cgrc_conn(c) >= 0 && c == c->engine->default_con)
+	int ret = cgrc_conn(c);
+	if (ret >= 0 && c == c->engine->default_con)
 		return cgrc_start_listen(c);
-	return -1;
+	return ret;
 }
 
 #ifdef HAVE_TIMER_FD