Add missing BSD-3-Clause license of tmt.c

confluent_vtbufferd/tmt.c has a BSD-3-Clause license as described in
confluent_vtbufferd/NOTICE, too.

confluent_vtbufferd/confluent_vtbufferd.spec.tmpl

@@ -9,7 +9,7 @@ Name: %{name}
 Version: %{version}
 Release: %{release}
 Source0: %{name}-%{version}.tar.gz
-License: Apache-2.0
+License: Apache-2.0 AND BSD-3-Clause
 Group: Development/Libraries
 Vendor: Lenovo HPC Organization <hpchelp@lenovo.com>
 Url: https://github.com/lenovo/confluent/