add n2 handover to same cell

[sgarg00]

Originally reported by Cédric Roux on 2026-05-06 — GitLab #1085

this is most probably needed for pdcp COUNT reset

this may be needed for nr-dc SCG Failure Information recovery (i struggle with this right now)

there is this code in nr_HO_N2_trigger_telnet(), not sure that it works:

  // Simulate handover on the same cell (testing purposes)
  if (neighbour_pci == scell_pci) {
    LOG_I(NR_RRC, "UE %d: trigger handover on the same cell PCI=%d\n", rrc_ue_id, neighbour_pci);
    nr_neighbour_cell_t neighbourConfig = {
        .gNB_ID = du->gNB_DU_id,
        .nrcell_id = pcell->info.cell_id,
        .physicalCellId = pcell->info.pci,
        .plmn = pcell->info.plmn,
        .subcarrierSpacing = pcell->info.mode == NR_MODE_TDD ? pcell->info.tdd.dlul.scs : pcell->info.fdd.dl.scs,
    };
    nr_rrc_trigger_n2_ho(rrc, UE, &neighbourConfig);
    return;
  }

writing something similar to deal with scg failure information leads to:

SCG failure triggered!!
[NR_RRC] measId received 1
[NR_RRC] UE  trigger handover on the same cell
[NR_RRC] Handover Preparation: send Handover Required (target gNB ID=3584, PCI=1)
[NGAP]   Handover Resource Allocation initiating message
[NGAP]   Received NG Handover Request from AMF OAI-AMF (ID=16)
[RRC]    UE context already exists for AMF UE NGAP ID 16, cannot process handover request
[NR_RRC] Send NG Handover Failure message (amf_ue_ngap_id 16) with cause 7 
 [NGAP]   Failed to find UE context associated with amf_ue_ngap_id=16

i attach a small pcap, in case

extract.pcap

I have a pcap from 06-2025 where I did a n2 handover to self to reset COUNT (by hacking the code at that time), so to me in principle it should be allowed