split off osmo-sgsn: remove files, apply build

Change-Id: I5d27ff93e56cd13e0e70edd15e2080201e35e91f
diff --git a/tests/gbproxy/gbproxy_test.c b/tests/gbproxy/gbproxy_test.c
index 577daa9..9672dcb 100644
--- a/tests/gbproxy/gbproxy_test.c
+++ b/tests/gbproxy/gbproxy_test.c
@@ -49,6 +49,8 @@
 
 #define MATCH_ANY (-1)
 
+void *tall_bsc_ctx;
+
 struct gbproxy_config gbcfg = {0};
 
 struct llist_head *received_messages = NULL;