Licence change

[jrybar-rh]

Is your feature request related to a problem? Please describe.
According to automated licence check performed on lsof sources, the following licences are used: Sendmail, BSD, GPL and Henry Spencer/Purdue (the one containing "This software is not subject to any license of the American Telephone...").

The last one is GPL-ish-friendly and can probably be changed to GPL, especially when the licence used is archaic, obsoleted and "unsanitized". The lack of specifics of the "Purdue" -or whatever it's called- licence used may cause unease with FOSS software distribution, as the licences tend to be listed in package description among distros, and SPDX form equivalent.