cu_cp_types: add target DU index to Inter DU HO command

Author: andrepuschmann

include/srsran/cu_cp/cu_cp_types.h

@@ -516,6 +516,7 @@ struct cu_cp_inactivity_notification {
 
 struct cu_cp_inter_du_handover_request {
   ue_index_t source_ue_index = ue_index_t::invalid;
+  du_index_t target_du_index = du_index_t::invalid;
   pci_t      neighbor_pci    = INVALID_PCI;
 };