[PATCH] selinux: Clear selinux_enabled flag upon runtime disable.

Clear selinux_enabled flag upon runtime disable of SELinux by userspace,
and make sure it is defined even if selinux= boot parameter support is
not enabled in configuration.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Tested-by: Jon Smirl <jonsmirl@gmail.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>