hnbgw: test for RUA Disconnect when there is no CNRelated: OS#6283Related: osmo-hnbgw Iafb30c31a4c5db53ecdda99a0e0b5937b71e362cTweaked-by: Oliver Smith <osmith@sysmocom.de>Change-Id: I2b5c024a395e736538c0c37db40d34f3b8d99991