sgsn: Add gprs_subscriber.c

This patch adds GPRS specific functions for gsm_subscriber objects
(allocation, retrieval, deletion) and subscriber data
requests/updates. The sgsn_update_subscriber_data callback is used to
notify the sgsn about updates and is extended by a parameter that
passes a reference to a gsm_subscriber.

Sponsored-by: On-Waves ehf
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index 75eafdd..f937362 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -22,7 +22,7 @@
 osmo_sgsn_SOURCES =	gprs_gmm.c gprs_sgsn.c gprs_sndcp.c gprs_sndcp_vty.c \
 			sgsn_main.c sgsn_vty.c sgsn_libgtp.c \
 			gprs_llc.c gprs_llc_parse.c gprs_llc_vty.c crc24.c \
-			sgsn_ctrl.c sgsn_auth.c
+			sgsn_ctrl.c sgsn_auth.c gprs_subscriber.c
 osmo_sgsn_LDADD = 	\
 			$(top_builddir)/src/libcommon/libcommon.a \
 			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS)