Make libradius optional

Signed-off-by: Garrett Cooper <yanegomi@gmail.com>
Merge branch 'atf-tools-regression-convert' of github.com:yaneurabeya/freebsd into atf-tools-regression-convert
Merge branch 'atf-tools-regression-convert' of github.com:yaneurabeya/freebsd into atf-tools-regression-convert