The function rrc_gNB_process_RRCReconfigurationComplete() does almost
nothing, we can delete it.
The variable name ue_reconfiguration_after_reestablishment_counter is
misleading, as it counts all reconfigurations; rename to make it clear.
- adds function to retrieve the only UE's RNTI
- adds function to trigger reestablishment for the only UE present, or a
specific via its RNTI
- adds function to verify the reestablishment counters