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/testsuite.at b/openbsc/tests/testsuite.at
index dab9568..6470ab9 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -124,3 +124,8 @@
 AT_CHECK([$abs_top_builddir/tests/mm_auth/mm_auth_test], [], [expout], [ignore])
 AT_CLEANUP
 
+AT_SETUP([xid])
+AT_KEYWORDS([xid])
+cat $abs_srcdir/xid/xid_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/xid/xid_test], [], [expout], [ignore])
+AT_CLEANUP