net/libdnet: Update version 1.12=>1.13

I have reviewed the code of net/libdnet. And created a fork as the
development seems stalled by the original author.

• Removed all the codes not related to FreeBSD
• Fix configure script to find related header files and now it builds relevant source files instead of *-none.c files
• Modernized all build tools configuration file and removed unnecessary files
• Works at least with PF. Still not working with ipfw2/ipfilter.

The repo location is:
https://github.com/5u623l20/libdnet/

PR: 236642
Submitted by: bofh
Approved by: maintainer-timeout