When a phone loses connection, it should not simply be removed but first
CU should be informed which will send a ContextRelCmd. Correspondingly,
when the RRC releases the UE, it does not send a UE Context Release Req

* remove PDCP/RRC contexts
* inform the FlexRAN controller

sctp_create_new_listener() takes a parameter server_type which is NOT
the IP version but whether it is an SCTP multihoming server. There was a
bug that when multihoming is not wanted, it created an IPv6 socket
instead of IPv4. This commit fixes this.

IPv6 is not supported yet.

* MAC differentiates between DU/eNB
* sends ITTI message to DU task for F1AP_UE_CONTEXT_RELEASE_REQ
* message is dispatched to correctly in DU_TASK
* sender correctly fills IDs and cause and sends

* RRC and MAC might sort users differently
* therefore, we have to "reverse lookup" the MAC ID from the RNTI when filling
  user info
* For this purpose, add RAN API function flexran_get_mac_ue_id_rnti()

* F1AP has to read MCC/MNC from list
* Do not stop if MACRLC list is not present in conf, it might be a CU

OER can be disable with the switch -DASN_DISABLE_OER_SUPPORT. In F1AP,
disabling OER leads to a typedef void a_type; leading to lots of compilation
errors because of illegal void variable declarations. This commit leaves OER
support enabled, avoiding this error.

* remove a lot of white spaces
* many conflicts in enb_config.c

This makes it possible to stop the link_manager by joining its threads.