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/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index 06c12d7..c044f24 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -71,6 +71,8 @@
 	gprs_gmm.c \
 	gprs_sgsn.c \
 	gprs_sndcp.c \
+	gprs_sndcp_comp.c \
+	gprs_sndcp_pcomp.c \
 	gprs_sndcp_vty.c \
 	gprs_sndcp_xid.c \
 	sgsn_main.c \