gb/gprs_bssgb: ensure the fc timer has been stopped when freeing bssgp_bvc

Change-Id: Id03ebef31bb513e2b3b5bc709a91e9352ebbbc79
diff --git a/src/gb/gprs_bssgp.c b/src/gb/gprs_bssgp.c
index e5b4380..8b8d534 100644
--- a/src/gb/gprs_bssgp.c
+++ b/src/gb/gprs_bssgp.c
@@ -171,6 +171,8 @@
 {
 	if (!ctx)
 		return;
+
+	osmo_timer_del(&ctx->fc->timer);
 	rate_ctr_group_free(ctx->ctrg);
 	llist_del(&ctx->list);
 	talloc_free(ctx);