Adding LLC-XID encoder / decoder and unit test

The lle-xid encoder/decoder is needed to encode and decode llc
xid parameter messages. We need this to exchange sndcp-parameters
(SNDCP-XID) and also simple parameters such as encryption IOVs

Change-Id: Ia06e4cb08bf9b48c2a4682606d1b1a91d19a9d37
diff --git a/openbsc/tests/xid/xid_test.ok b/openbsc/tests/xid/xid_test.ok
new file mode 100644
index 0000000..4cf825c
--- /dev/null
+++ b/openbsc/tests/xid/xid_test.ok
@@ -0,0 +1,12 @@
+Testing LLC XID-Decoder/Encoder
+Decoded:
+Result length=64
+Encoded:  01001605f01a05f0acd8000100023182022789ffe0000f00a8000000010101000201020003010300040104000501050006000701070008010880000412004007
+Rencoded: 01001605f01a05f0acd8000100023182022789ffe0000f00a8000000010101000201020003010300040104000501050006000701070008010880000412004007
+
+Testing LLC XID-Encoder
+Data to encode:
+Encoded:  108c1443434343430b4242420541 (14 bytes)
+Expected: 108c1443434343430b4242420541 (14 bytes)
+
+Done