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.

The PROTO_AGENT variable holding the channel for various was named as the same
one for FlexRAN. In C, global variables with the same name are merged into one,
which had the effect that the same queues where used for PROTO_AGENT and
FlexRAN, locking the FlexRAN RX thread. Renaming the PROTO_AGENT variable (it
was introduced second) resolves this issue.

This commit cleans up the link_manager interface:
* don't provide peer_addr/port in create_link_manager() (for TCP/SCTP it is not
  needed, so in the UDP case in needs to be set explicitly)
* Make FlexRAN connect again (correct hardcoded address)
* Fix FlexRAN: retain the manager pointer
* Fix FlexRAN: store receive_queue pointer
* the link_manager's sender thread passes the correct peer_addr/port for the
  UDP case