MAC/do: Re-order jail methods more logically, rename

No functional change intended.

Reviewed by: bapt
Approved by: markj (mentor)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D47606

(cherry picked from commit 2b2c19b7f697cc88d4da3e8e13051139cd0a4f96)