selinux: avoid implicit conversions regarding enforcing status

Use the type bool as parameter type in
selinux_status_update_setenforce().  The related function
enforcing_enabled() returns the type bool, while the struct
selinux_kernel_status member enforcing uses an u32.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
[PM: subject line tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>