SELINUX: Call setuid(0)/setgid(0) to also set the real IDs to root
libselinux uses many access(2) calls and access() uses the real UID,
not the effective UID for the check. Therefore, the setuid selinux_child,
which only has effective UID of root would fail the check.
Reviewed-by: Michal Židek <firstname.lastname@example.org>
(cherry picked from commit 486f0d5227a9b81815aaaf7d9a2c39aafcbfdf6a)