SNDCP: add RFC1144 header compression functionality

- Add module to handle compression entities
- Add module to control header compression
- Introduce VTY commands for heade compression configuration
- Add changes in sndcp and llc to integrate header compression

Change-Id: Ia00260dc09978844c2865957b4d43000b78b5e43
diff --git a/openbsc/tests/sgsn/Makefile.am b/openbsc/tests/sgsn/Makefile.am
index bab3f0e..1447577 100644
--- a/openbsc/tests/sgsn/Makefile.am
+++ b/openbsc/tests/sgsn/Makefile.am
@@ -59,6 +59,8 @@
         $(top_builddir)/src/gprs/gprs_llc_xid.o \
 	$(top_builddir)/src/gprs/gprs_sndcp_xid.o \
         $(top_builddir)/src/gprs/slhc.o \
+        $(top_builddir)/src/gprs/gprs_sndcp_comp.o \
+        $(top_builddir)/src/gprs/gprs_sndcp_pcomp.o \
 	$(top_builddir)/src/libcommon/libcommon.a \
 	$(LIBOSMOABIS_LIBS) \
 	$(LIBOSMOCORE_LIBS) \