code: def attach_intf_router(self, tenant_id, tenant_name, router_id):
          
          in_sub = self.get_in_subnet_id(tenant_id)
          out_sub = self.get_out_subnet_id(tenant_id)
          # Modify Hard coded Name fixme
          subnet_lst = set()
          subnet_lst.add(in_sub)
          subnet_lst.add(out_sub)
          ret = self.os_helper.add_intf_router(router_id, tenant_id, subnet_lst)
          return ret, in_sub, out_sub
docs: Routine to attach the interface to the router.