This commit adds initial support to encode/decode SBc-AP messages in the
form of a library, under src/sbcap/ (includes in
include/osmocom/sbcap/).
asn1c is used to generate all suport code and structures for ASN.1 APER
encoding/decoding, based on asn files obtained from 3GPP TS 29.168 and
stored under src/sbcap/asn1/.
Currently, mainstream asn1c doesn't yet support ASN.1 APER
encoding/decoding, hence mouse07410 's fork is used [1]. Furthermore,
several encdoing/decoding bugs where found during the process and fixed,
which means asn1.c git >= 30219de2d3da888b4f1eea0dd79f2a505000401a must
be used to generate proper code.
A new "make -C src/ gen" target is added which can be used to regenerate
all C code from the available ASN.1 files in src/sbcap/asn1/*.asn (after
properly setting configure.ac ASN_* variables if needed).
[1] https://github.com/mouse07410/asn1c
Related: OS#4945
Change-Id: If76f8619a9b2d46af6d94b8ae49348b8514e53aa
