Adding LLC-XID related modifications in LLC

With this commit the already existing XID mechanism has been
modified to suit the needs for the upcomming SNDCP-XID patches.

This commit should not break anything since it does not alter
the current behaviour (incoming XID is still just echoed, on
GMM-Reset a basic XID message is still echoed)

Change-Id: I65b9d625e72d3d61c99abdc7041773701d694d52
diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index b6036c7..74af159 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -30,6 +30,7 @@
 	$(top_builddir)/src/gprs/gprs_gb_parse.o \
 	$(top_builddir)/src/gprs/oap.o \
 	$(top_builddir)/src/gprs/oap_messages.o \
+        $(top_builddir)/src/gprs/gprs_llc_xid.o \
 	$(top_builddir)/src/libcommon/libcommon.a \
 	$(LIBOSMOABIS_LIBS) \
 	$(LIBOSMOCORE_LIBS) \