SELINUX: Check if SELinux is managed in selinux_child
    
    If SELinux policy is not managed at all, don't call any SELinux user
    handling functions and instead return that no update is needed.
    
    Pair-Programmed-With: Jakub Hrozek <jhrozek@redhat.com>
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3618