New port: devel/linux-ltp

The LTP testsuite contains a collection of tools for testing
the Linux kernel and related features. This package is intended
for testing the Linux kernel ABI provided by linux(4).

WWW: https://github.com/linux-test-project/ltp

Reviewed by: ngie, lwhsu (earlier version)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D20092