SPDX: Tag BSD-4.3TAHOE

TIL traceroute.8 has one of the oldest liceses, predating BSD-4-Clause!
The SPDX tag was not even on Wikipedia. These are all the files I could
find in the tree with git grep that look like the license reported on
the SPDX website, including one that was misfiled.

Ref: https://spdx.org/licenses/BSD-4.3TAHOE.html
MFC after: 3 days
Reported by: brooks
Reviewed by: brooks, carlavilla, imp, ivy
Approved by: carlavilla (mentor)
Differential Revision: https://reviews.freebsd.org/D50362

(cherry picked from commit 7098712bbfd60df9db324decbc1a5dd8f751356f)