Add comment on reestablishment in MAC-RRC DL handler

openair2/LAYER2/NR_MAC_gNB/mac_rrc_dl_handler.c

@@ -954,6 +954,8 @@ void dl_rrc_message_transfer(const f1ap_dl_rrc_message_t *dl_rrc)
     UE->reestablish_rlc = false;
   }
 
+  /* if we get the old-gNB-DU-UE-ID, this means there is a reestablishment
+   * ongoing. */
   if (dl_rrc->old_gNB_DU_ue_id != NULL) {
     AssertFatal(*dl_rrc->old_gNB_DU_ue_id != dl_rrc->gNB_DU_ue_id,
                 "logic bug: current and old gNB DU UE ID cannot be the same\n");