support routing control and user plane over different NS links
it's somewhat hidden in the NS spec (TS 48.016) that at least when the SNS-CONFIG procedure is in use, the SGSN can configure different NS links, e.g. one with data weight 0 and another one with control weight 0. This means that the control and data plane are to be running on differnent links.
This requires significant architectural changes in libosmogb and its data model to support.