net/freeradius3: Update MASTER_SITES

As ftp is indirectly becoming deprecated and less "common" switch to
http(s) and fallback to ftp. Use GitHub as primary site to offload
upstream main site, fallback if that fails to main site and try
https protocol before falling back to ftp. While at it remove
unofficial mirrors.

PR: 260302
Reported by: Shawn Webb
Approved by: arrowd (mentor), zi (maintainer timeout, 3 weeks)
Differential Revision: https://reviews.freebsd.org/D33691