trace2:gvfs:experiment: increase default event depth for unpack-tree data

trace2/tr2_tgt_event.c

@@ -36,7 +36,7 @@ static struct tr2_dst tr2dst_event = {
  * event target.  Use the TR2_SYSENV_EVENT_NESTING setting to increase
  * region details in the event target.
  */
-static int tr2env_event_max_nesting_levels = 2;
+static int tr2env_event_max_nesting_levels = 4;
 
 /*
  * Use the TR2_SYSENV_EVENT_BRIEF to omit the <time>, <file>, and