leak-detective: Use passed callback to report leaks

This prevented `stroke memusage` from reporting the leaks on the
console.  Instead, they were sent to the callbacks set up by libstrongswan.

Fixes a426851f63 ("leak-detective: Use callback functions to report
leaks and usage information").

src/libstrongswan/utils/leak_detective.c

@@ -691,8 +691,8 @@ static int print_traces(private_leak_detective_t *this,
 			{
 				if (!thresh_count || entry->count >= thresh_count)
 				{
-					this->report_cb(this->report_data, entry->count,
-									entry->bytes, entry->backtrace, detailed);
+					cb(user, entry->count, entry->bytes, entry->backtrace,
+					   detailed);
 				}
 			}
 		}