Use list of UEs during RA instead of array of RA processes

- rewrite add_UE_to_list() and rewrite remove_UE_from_list() to simplify
  list handling
- return pointer from get_new_nr_ue_inst(); it's completely freed by
  delete_nr_ue_data()
- have add_new_UE_RA() add UE context to access list; remove with
  nr_release_ra_UE()
- have add_connected_nr_ue() only add UE to connected list; to move from
  access to connected use transition_ra_connected_nr_ue(); remove with
  mac_remove_nr_ue() as previously
- free memory on problems during RA
- add some documentation
- in NSA/HO: check for pre-configured RA process
- there are asserts in all functions to clarify when a UE has RA

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -609,9 +609,6 @@ static void pf_dl(module_id_t module_id,
 
   /* Loop UE_info->list to check retransmission */
   UE_iterator(UE_list, UE) {
-    if (!UE->Msg4_MsgB_ACKed)
-      continue;
-
     NR_UE_sched_ctrl_t *sched_ctrl = &UE->UE_sched_ctrl;
     NR_UE_DL_BWP_t *current_BWP = &UE->current_DL_BWP;