fix vty: show talloc-context all

Without "null tracking" enabled, the VTY 'show talloc-ctx all' shows
nothing at all.

Since the talloc_asn1_ctx is "created in NULL ctx", it was not visible
in any talloc reports before this patch.

This patch uncovers a slur of leaks, which accumulate in
talloc_asn1_ctx. Fixes follow.

Related: SYS#6297
Change-Id: I5cb4e9a3b393100877f03d68a09acf5817c5a878
---
M src/osmo-hnbgw/hnbgw.c
1 file changed, 21 insertions(+), 0 deletions(-)

diff --git a/src/osmo-hnbgw/hnbgw.c b/src/osmo-hnbgw/hnbgw.c
index bd45dda..50ada60 100644
--- a/src/osmo-hnbgw/hnbgw.c
+++ b/src/osmo-hnbgw/hnbgw.c
@@ -729,6 +729,8 @@
 	struct osmo_stream_srv_link *srv;
 	int rc;
 
+	talloc_enable_null_tracking();
+
 	tall_hnb_ctx = talloc_named_const(NULL, 0, "hnb_context");
 	talloc_asn1_ctx = talloc_named_const(NULL, 1, "asn1_context");
 	msgb_talloc_ctx_init(tall_hnb_ctx, 0);

