load_balancer: open db connection from every process

This ensures that the `mi("lb_reload")` command runs properly from
whatever process the job is dispatched from.

Many thanks to Antonis Psaras (@apsaras on GitHub) for reporting it.
Close #3488

modules/load_balancer/load_balancer.c

@@ -479,17 +479,17 @@ static int mod_init(void)
 
 static int child_init(int rank)
 {
+	/* init DB connection */
+	if ( lb_connect_db(&db_url)!=0 ) {
+		LM_CRIT("cannot initialize database connection\n");
+		return -1;
+	}
 	return 0;
 }
 
 
 static int mi_child_init( void )
 {
-	/* init DB connection */
-	if ( lb_connect_db(&db_url)!=0 ) {
-		LM_CRIT("cannot initialize database connection\n");
-		return -1;
-	}
 	return 0;
 }