Harmonize UE context setup resp bearer handling

This is preparatory work to handle the UE context setup response from
the target DU. There are two cases:

- "Initial" UE context setup response (during connection setup): we need
  to inform the CU-UP via an E1 message of the new bearers (GTP tunnel
  update)
- F1 handover:  we need to inform the CU-UP via an E1 message that there
  are DRBs to reestablish

There are two different functions, e1_send_bearer_updates() and
cuup_notify_reestablishment(), to do this. Harmonize the code, before
implementing the actual handover logic in the next commit.

openair2/RRC/NR/rrc_gNB.c

@@ -1851,11 +1851,17 @@ static void rrc_CU_process_ue_context_setup_response(MessageDef *msg_p, instance
     xer_fprint(stdout, &asn_DEF_NR_CellGroupConfig, UE->masterCellGroup);
 
   if (resp->drbs_to_be_setup_length > 0) {
+    int num_drb = get_number_active_drbs(UE);
+    DevAssert(num_drb == 0 || num_drb == resp->drbs_to_be_setup_length);
+
     /* Note: we would ideally check that SRB2 is acked, but at least LiteOn DU
      * seems buggy and does not ack, so simply check that locally we activated */
     AssertFatal(UE->Srb[1].Active && UE->Srb[2].Active, "SRBs 1 and 2 must be active during DRB Establishment");
     store_du_f1u_tunnel(resp->drbs_to_be_setup, resp->drbs_to_be_setup_length, UE);
+    if (num_drb == 0)
       e1_send_bearer_updates(rrc, UE, resp->drbs_to_be_setup_length, resp->drbs_to_be_setup);
+    else
+      cuup_notify_reestablishment(rrc, UE);
   }
 
   rrc_gNB_generate_dedicatedRRCReconfiguration(rrc, UE);

openair2/RRC/NR/rrc_gNB_radio_bearers.c

@@ -181,6 +181,15 @@ uint8_t get_next_available_drb_id(gNB_RRC_UE_t *ue)
   return DRB_INACTIVE;
 }
 
+int get_number_active_drbs(gNB_RRC_UE_t *ue)
+{
+  int n = 0;
+  for (int i = 0; i < MAX_DRBS_PER_UE; ++i)
+    if (ue->established_drbs[i].status != DRB_INACTIVE)
+      n++;
+  return n;
+}
+
 bool drb_is_active(gNB_RRC_UE_t *ue, uint8_t drb_id)
 {
   drb_t *drb = get_drb(ue, drb_id);

openair2/RRC/NR/rrc_gNB_radio_bearers.h

@@ -61,6 +61,9 @@ drb_t *generateDRB(gNB_RRC_UE_t *ue,
 /// @brief return the next available (inactive) DRB ID of UE ue
 uint8_t get_next_available_drb_id(gNB_RRC_UE_t *ue);
 
+/// @brief returns the number of active DRBs for this UE
+int get_number_active_drbs(gNB_RRC_UE_t *ue);
+
 /// @brief check if DRB with ID drb_id of UE ue is active
 bool drb_is_active(gNB_RRC_UE_t *ue, uint8_t drb_id);