split off osmo-sgsn: remove files, apply build

Change-Id: I5d27ff93e56cd13e0e70edd15e2080201e35e91f
diff --git a/src/gprs/gprs_sgsn.c b/src/gprs/gprs_sgsn.c
index de79afb..560485d 100644
--- a/src/gprs/gprs_sgsn.c
+++ b/src/gprs/gprs_sgsn.c
@@ -31,6 +31,7 @@
 #include <osmocom/gprs/gprs_bssgp.h>
 #include <osmocom/gsm/protocol/gsm_04_08_gprs.h>
 #include <osmocom/gsm/apn.h>
+#include <osmocom/gsm/gsm_utils.h>
 
 #include <openbsc/gprs_subscriber.h>
 #include <openbsc/debug.h>
@@ -56,6 +57,7 @@
 #define GPRS_LLME_CHECK_TICK 30
 
 extern struct sgsn_instance *sgsn;
+extern void *tall_bsc_ctx;
 
 LLIST_HEAD(sgsn_mm_ctxts);
 LLIST_HEAD(sgsn_ggsn_ctxts);