Introduce separate gNB-CU-UP ID in configuration

3GPP has the concept of a gNB-CU-UP ID and a (separate) gNB ID (for gNB,
CU-CP). This commit introduces the gNB-CU-UP as a separate ID that has to be
set in the configuration file when running as a CU-UP. For the
CU/monolithic gNB, it is optional (but needs to be the same as the
gNB-ID if specified).

The CU-UP ID is necessary, as some entities, e.g., the e2 agent, need to
signal both IDs, e.g., to reconcile a CU-CP and (multiple) CU-UP(s)
belonging together.

executables/nr-softmodem.c

@@ -402,9 +402,9 @@ static int create_gNB_tasks(ngran_node_t node_type, configmodule_interface_t *cf
 
     // If CU
     if (node_type == ngran_gNB_CU || node_type == ngran_gNB) {
-      MessageDef *msg = RCconfig_NR_CU_E1(false);
+      MessageDef *msg = RCconfig_NR_CU_E1(NULL);
       instance_t inst = 0;
-      createE1inst(UPtype, inst, &E1AP_REGISTER_REQ(msg).net_config, NULL);
+      createE1inst(UPtype, inst, E1AP_REGISTER_REQ(msg).gnb_id, &E1AP_REGISTER_REQ(msg).net_config, NULL);
       cuup_init_n3(inst);
       RC.nrrrc[gnb_id_start]->e1_inst = inst; // stupid instance !!!*/