SNDCP: add SNDCP-XID encoder/decoder and unit test

The SNDCP-XID (or layer-3 xid) is used to exchange layer-3 parameters
such as compression. The encoder encodes a bytestream that is then
sent as regular XID field from LLC.

We will need the SNDCP-XID to negotiate the parameters for our
upcomming GPRS data and header compression features

Change-Id: If2d63fe2550864cafef3156b1dc0629037c49c1e
12 files changed
tree: d3cf6edb86ad200de2689eabc45b6f70afa38264
  1. contrib/
  2. debian/
  3. openbsc/
  4. .gitignore
  5. .gitreview
  6. .mailmap