pkgbase: Create a FreeBSD-telnet package

both telnet and telnetd aren't that useful nowadays but some
might want them.
Create a FreeBSD-telnet package so users have a choice to have
them or not.

Differential Revision: https://reviews.freebsd.org/D31791
Reviewed by: emaste

(cherry picked from commit c7fd29f0f29ae3eb9d86cc019f6c1bab35634548)