split off osmo-sgsn: remove files, apply build

Change-Id: I5d27ff93e56cd13e0e70edd15e2080201e35e91f
diff --git a/src/gprs/gtphub_vty.c b/src/gprs/gtphub_vty.c
index a30ad2a..d611b1f 100644
--- a/src/gprs/gtphub_vty.c
+++ b/src/gprs/gtphub_vty.c
@@ -37,6 +37,7 @@
  * globals. */
 #include <openbsc/sgsn.h>
 extern struct sgsn_instance *sgsn;
+extern void *tall_bsc_ctx;
 
 static struct gtphub *g_hub = 0;
 static struct gtphub_cfg *g_cfg = 0;