traceroute: Add SPDX-License-Identifier tags

[tuukka.pasanen_ilmi.fi]

Summary

This commit contains some BSD-4-Clause. First is normal SPDX-License-Identifier-tag BSD-4-Clause but it could be also BSD-4-Clause-UC but as it's acknowledgement is Lawrence Berkeley Laboratory so it is not fitting that one directly.

Also BSD-4-Clause-Shortened should be checked as there is not many of them available to compare with.

Seems that BSD-2-Clause is missing in commit message.

Sponsored by: The FreeBSD Foundation