RRC Bugfix: Propagate DU association ID from PDCP to RRC via ITTI message header

When processing UL RRC messages from PDCP, the DU association ID (assoc_id)
was not being propagated to RRC, resulting in assoc_id being 0 in
rrc_gNB_decode_dcch.

Fix by setting originInstance in the ITTI message header to the stored
du_assoc_id from ue_data when PDCP creates the F1AP_UL_RRC_MESSAGE.

openair2/LAYER2/nr_pdcp/nr_pdcp_oai_api.c

@@ -506,6 +506,7 @@ srb_found:
      * RRC, the RLC-PDCP interface does not transport this information */
     f1_ue_data_t ue_data = cu_get_f1_ue_data(ue->ue_id);
     ul_rrc->gNB_DU_ue_id = ue_data.secondary_ue;
+    message_p->ittiMsgHeader.originInstance = ue_data.du_assoc_id;
     ul_rrc->srb_id = srb_id;
     ul_rrc->rrc_container = malloc(size);
     AssertFatal(ul_rrc->rrc_container != NULL, "OUT OF MEMORY\n");