domain: init db connection for RPC process

- make mi commands to work properly via RPC interface
- reported by Juha Heinanen

modules_k/domain/domain_mod.c

@@ -212,7 +212,7 @@ error:
 static int child_init(int rank)
 {
 	/* Check if database is needed by child */
-	if ( db_mode==0 && rank>0 ) {
+	if ( (db_mode==0 && rank>0) || (rank==PROC_RPC) ) {
 		if (domain_db_init(&db_url)<0) {
 			LM_ERR("Unable to connect to the database\n");
 			return -1;