Free DU at CU on lost connection, store assoc ID

- store the assoc ID of a UE at the RRC
- if F1 receives an SCTP shutdown, it removes the endpoint
- F1 will also send an "F1 Lost Connection" message to the RRC
- it is not yet possible to reconnect a DU after it had already been
  connected at the CU, since the CU F1AP task will try to rebind GTP,
  which fails

openair2/F1AP/f1ap_common.c

@@ -63,3 +63,13 @@ void createF1inst(instance_t instanceP, f1ap_setup_req_t *req, f1ap_net_config_t
     f1_inst[0]->net_config = *nc;
   pthread_mutex_unlock(&f1_inst_mtx);
 }
+
+void destroyF1inst(instance_t instance)
+{
+  DevAssert(instance == 0);
+  pthread_mutex_lock(&f1_inst_mtx);
+  AssertFatal(f1_inst[0] != NULL, "Attempted to free uninitialized F1 instances\n");
+  free(f1_inst[instance]);
+  f1_inst[instance] = NULL;
+  pthread_mutex_unlock(&f1_inst_mtx);
+}