Dummy CN: Handle RANAP payload of DISCONNET.ind

In case of RANAP Release Complete, the DISCONNECT contains RANAP payload that
we'd like to parse and handle.
diff --git a/src/tests/dummy_cn_sua.c b/src/tests/dummy_cn_sua.c
index 024d514..de850a7 100644
--- a/src/tests/dummy_cn_sua.c
+++ b/src/tests/dummy_cn_sua.c
@@ -277,6 +277,8 @@
 	case OSMO_PRIM(OSMO_SCU_PRIM_N_DISCONNECT, PRIM_OP_INDICATION):
 		/* indication of disconnect */
 		printf("N-DISCONNECT.ind(%u)\n", prim->u.disconnect.conn_id);
+		ue = ue_conn_ctx_find(link, prim->u.disconnect.conn_id);
+		rc = cn_ranap_rx_co(ue, msgb_l2(oph->msg), msgb_l2len(oph->msg));
 		break;
 	case OSMO_PRIM(OSMO_SCU_PRIM_N_DATA, PRIM_OP_INDICATION):
 		/* connection-oriented data received */