libgb: remove dependencies to openbsc/vty.h and openbsc/gsm_data.h

Rather than using openbsc internal data/functions, we now use only
internal and libosmocore-provided ones.
diff --git a/openbsc/src/gprs/gb_proxy_main.c b/openbsc/src/gprs/gb_proxy_main.c
index b853fbf..5f67a71 100644
--- a/openbsc/src/gprs/gb_proxy_main.c
+++ b/openbsc/src/gprs/gb_proxy_main.c
@@ -229,7 +229,7 @@
 	if (rc < 0)
 		exit(1);
 
-	bssgp_nsi = gprs_ns_instantiate(&proxy_ns_cb);
+	bssgp_nsi = gprs_ns_instantiate(&proxy_ns_cb, tall_bsc_ctx);
 	if (!bssgp_nsi) {
 		LOGP(DGPRS, LOGL_ERROR, "Unable to instantiate NS\n");
 		exit(1);