net-mgmt/rrdbot: switch to active fork

Since the original RRDBot project has been abandoned a long time ago,
the proposal is to switching to an active fork https://github.com/REANNZ/rrdbot
that has minor bug fixes and enhancements.

The REANNZ (Research and Education Advanced Network New Zealand) is a new
Zealand's National Research and Education Network. They fork net-mgmt/rrdbot
in 2015 and start doing changes and improvements in the existing source code
You can see the git history in the github repo[1] (159 commits), but I also kept
a full diff between the previous official version and the new repo version [2].

[1] https://github.com/REANNZ/rrdbot/commits/master
[2] https://people.freebsd.org/~rodrigo/rrdbot-0.9.7_switch_orig.diff

The new repo doesn't provide official release numbers, so we kept the latest version
number completed by the packaging date in the dYYYYMMDD format.

PR: 244757
Submitted by: Alexander Moisseev <moiseev@mezonplus.ru>