ENDC for 5G NSA support (preparatory work): Basic implementation of x2ap_eNB_generate_ENDC_x2_setup_request() and x2ap_gNB_handle_ENDC_x2_setup_request()

Dual connectivity: Basic implementation of x2ap_eNB_handle_senb_addition_request and x2ap_eNB_generate_senb_addition_request_ack

- basic version of x2ap_eNB_generate_senb_addition_request with dumb values
- skeleton functions:
    - x2ap_eNB_handle_senb_addition_request
    - x2ap_eNB_handle_senb_addition_request_acknowledge
    - x2ap_eNB_handle_senb_addition_request_reject

The 5G phone OPPO has a very big UE capability (> 2KB).

We need bigger buffers to transfer this, especially in x2 handover.

Also the sctp messages need a bigger buffer.

Note: in sctp, we didn't check for partial messages, it's now
      done. When detected, we exit. To be redone differently
      if needed. (Look for "if (!(flags & MSG_EOR))".)

To be tested: Add code for measurement report based on the neighbouring cells after x2 setup, ocs/ocn for multiple cells

ReFix Coverity Scan CID 339937 (Overrunning array x2ap_messages_callback of 27 24-byte elements at element index 27 (byte offset 648) using index pdu.choice.successfulOutcome.procedureCode (which evaluates to 27).)

This commit introduces X2AP timers (t_reloc_prep, tx2_reloc_overall).
You need to set the values in the configuration file.

X2AP can be enabled or disabled in the configuration file too (disabled
by default).

Some deadcode was removed.

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

Some deadcode was removed.

The implementation of the ID management is not finished.
It will only work if the handover is successful. No error
recovery has been done. For error recovery, we need to
implement the X2AP timers. As it is, in case of error, an ID
might very well never be released.

It has been tested with 1 and 2 UEs doing handover more or less
at the same time.

- manage target eNB based on target cell id received by measurement report
  for Handover Request
- manage source eNB based on association id for Handover Request Ack
- use only x2ap instance and not x2ap data instance points to x2ap instance

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

remove L1L2 task, also remove some call to send messages to UNKNOWN_TASK, removed in new itti. Align LOG in rlc sources with new LOG code (remove DEBUG_RLC...)

For whatever reason most of the files had their permission
changed from 644 to 755, which is not wanted.

S1AP PATH SWITCH REQUEST/REQUEST ACK/FAILURE
RRC MEASUREMENT REPORT
MINOR CHANGES IN MAC LAYER

If the IP address for X2AP is not good, the error message reported
was very unclear. Attempt to make it better.

SCTP: one to many sockets implementation

Use common log mechanism in layer 3, mapping specific macros to common ones and extending common log utilities to support specific layer3 requirements

1. It's no need to modify LTE-RRC's ASN.1 file for enabling option group
   feature in generate_asn1.
2. It's no need to patch the C header files generated from
   LTE-RRC/S1AP/X2AP's ASN.1 in fix_asn1.
3. It's no need to pre-process S1AP/X2AP's ASN.1 for enabling information
   object class feature by asn1tostruct.py.

This commit requires an un-official version of asn1c which are
collaboration of asn1c community members and `build_helper` is modified
in this commit accordingly :

  https://github.com/brchiu/asn1c/tree/velichkov_s1ap_plus_option_group

This asn1c can also convert ASN.1 of 5G NR RRC (38.331, v15.1.0) and
generate C files with -findirect-choice command line option without
tweaking ASN.1 file.

Examples for how to use this asn1c for S1AP are in S1AP files, e.g.
s1ap_eNB_nas_procedures.c and s1ap_eNB_handler.c.

There is an modified openair-cn (based on tag 0.5.0) with this new asn1c at :

  https://github.com/brchiu/openair-cn/tree/new-asn1c

Basic S1AP interaction and data transfer operation between OAI eNB and
this modified openair-cn has been tested.

Note: Community version of asn1c is keeping evolved to provide better usage.

This feature requires an un-official version of asn1c :

https://github.com/velichkov/asn1c/tree/s1ap

Fix #582, RTAI, RTAI_ENABLED, ENABLE_RTAI_CLOCK, RTAI_ISNT_POSIX, _RTAI_MATH_H, CELLULAR, TIMER_ONESHOT_MODE, EMOS, EMOS_CHANNEL, OAI_EMU, OPENAIR_EMU, PHY_ABSTRACTION, PHY_ABSTRACTION_UL removed