Upstream kindly made a new release including the following LICENSE file:
```
The individual files in this distribution are copyright their
original contributors or assignees.
Including:
Copyright (c) 1994-2020, Simon J Gerraty
Copyright (c) 2010-2018, Juniper Networks, Inc.
Copyright (c) 1988-1993Kind
The Regents of the University of California.
Note: some of the *.mk files here were originally derrived from
early NetBSD bsd.*.mk and do not carry any explicit copyright notice,
or license terms, as is the custom in the BSD world for makefiles.
The contributions from Juniper Networks are under:
SPDX-License-Identifier: BSD-2-Clause
and you can consider that the operative license.
```