Add test to trigger re-establishment to RFSIM F1 CI

* trigger re-establshemnt on DU: reset RLC counters on DRB 1
  for OAI UE, since SRB 1 does not work for lack of periodic
  measurements reports
* how is the re-establishment triggered?
  * a transmission on DRB 1 occurs
  * detection of a mismatch of RLC counters at the UE side
  * max number of RLC retransmissions reached
  * RLF detection
* verify re-establishment on CU: we ping the core from the UE; this
  sends packets on DRB, and because the sequence number mismatches, will
  trigger a reestablishment. We accept in the ping that a couple of
  packets might be lost; after ping is over, reestablishment must be
  done as well (else the ping will already fail).

openair2/LAYER2/nr_rlc/nr_rlc_oai_api.c

@@ -1096,8 +1096,14 @@ bool nr_rlc_update_id(int from_id, int to_id)
   return true;
 }
 
-/* This function is for testing purposes. At least on a COTS UE, it will
- * trigger a reestablishment. */
+/**
+ * @brief This function is for testing purposes.
+ *        Re-establishment is triggered by resetting RLC counters of the bearer,
+ *        which leads to UE reaching maximum RLC retransmissions, RLF detection
+ *        and RRC triggering re-sync. It is assumed that there is ongoing traffic on the bearer.
+ *        - With COTS UEs, triggers re-establishment on SRB 1, where periodical measurement reports are sent.
+ *        - With OAI UE, triggers re-establishment on DRB 1, assuming there is ongoing data traffic.
+ */
 void nr_rlc_test_trigger_reestablishment(int ue_id)
 {
   nr_rlc_manager_lock(nr_rlc_ue_manager);
@@ -1111,6 +1117,9 @@ void nr_rlc_test_trigger_reestablishment(int ue_id)
    * as the UE context is created. */
   nr_rlc_entity_t *ent = ue->srb[0];
   ent->reestablishment(ent);
+  /* Trigger re-establishment on OAI UE */
+  nr_rlc_entity_t *drb = ue->drb[0];
+  drb->reestablishment(drb);
   nr_rlc_manager_unlock(nr_rlc_ue_manager);
 }