core_unreal.c: Fix memory leak in ast_unreal_new_channels()

When the channel tech is multistream capable, the reference to
chan_topology was passed to the new channel.  When the channel tech
isn't multistream capable, the reference to chan_topology was never
released.  "Local" channels are multistream capable so it didn't
affect them but the confbridge "CBAnn" and the bridge_media
"Recorder" channels are not so they caused a leak every time one
of them was created.

Also added tracing to ast_stream_topology_alloc() and
stream_topology_destroy() to assist with debugging.

Resolves: #938
(cherry picked from commit d6ffbff333)

main/core_unreal.c

@@ -1169,7 +1169,7 @@ struct ast_channel *ast_unreal_new_channels(struct ast_unreal_pvt *p,
 	struct ast_assigned_ids id2 = {NULL, NULL};
 	int generated_seqno = ast_atomic_fetchadd_int((int *) &name_sequence, +1);
 	int i;
-	struct ast_stream_topology *chan_topology;
+	RAII_VAR(struct ast_stream_topology *, chan_topology, NULL, ast_stream_topology_free);
 	struct ast_stream *stream;
 
 	/* set unique ids for the two channels */
@@ -1221,7 +1221,6 @@ struct ast_channel *ast_unreal_new_channels(struct ast_unreal_pvt *p,
 		"%s/%s-%08x;1", tech->type, p->name, (unsigned)generated_seqno);
 	if (!owner) {
 		ast_log(LOG_WARNING, "Unable to allocate owner channel structure\n");
-		ast_stream_topology_free(chan_topology);
 		return NULL;
 	}
 
@@ -1295,7 +1294,7 @@ struct ast_channel *ast_unreal_new_channels(struct ast_unreal_pvt *p,
 	ast_channel_nativeformats_set(chan, p->reqcap);
 
 	if (ast_channel_is_multistream(chan)) {
-		ast_channel_set_stream_topology(chan, chan_topology);
+		ast_channel_set_stream_topology(chan, ao2_bump(chan_topology));
 	}
 
 	/* Format was already determined when setting up owner */

main/stream.c

@@ -641,27 +641,30 @@ struct ast_stream *ast_stream_create_resolved(struct ast_stream *pending_stream,
 static void stream_topology_destroy(void *data)
 {
 	struct ast_stream_topology *topology = data;
+	SCOPE_ENTER(4, "Topology: %p: %s\n", topology, ast_str_tmp(128, ast_stream_topology_to_str(topology, &STR_TMP)));
 
 	AST_VECTOR_CALLBACK_VOID(&topology->streams, ast_stream_free);
 	AST_VECTOR_FREE(&topology->streams);
+	SCOPE_EXIT_RTN("Destroyed: %p\n", topology);
 }
 
 #define TOPOLOGY_INITIAL_STREAM_COUNT 2
 struct ast_stream_topology *ast_stream_topology_alloc(void)
 {
 	struct ast_stream_topology *topology;
+	SCOPE_ENTER(4, "Topology Create\n");
 
 	topology = ao2_alloc_options(sizeof(*topology), stream_topology_destroy, AO2_ALLOC_OPT_LOCK_NOLOCK);
 	if (!topology) {
-		return NULL;
+		SCOPE_EXIT_RTN_VALUE(NULL, "Allocation failed\n");
 	}
 
 	if (AST_VECTOR_INIT(&topology->streams, TOPOLOGY_INITIAL_STREAM_COUNT)) {
 		ao2_ref(topology, -1);
-		topology = NULL;
+		SCOPE_EXIT_RTN_VALUE(NULL, "Vector init failed\n");
 	}
 
-	return topology;
+	SCOPE_EXIT_RTN_VALUE(topology, "Created: %p\n", topology);
 }
 
 struct ast_stream_topology *ast_stream_topology_clone(