selinux: preserve boolean values across policy reloads

At present, the userland policy loading code has to go through contortions to preserve
boolean values across policy reloads, and cannot do so atomically.
As this is what we always want to do for reloads, let the kernel preserve them instead.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Karl MacMillan <kmacmillan@mentalrootkit.com>
Signed-off-by: James Morris <jmorris@namei.org>