[PATCH] SELinux: add null device node to selinuxfs, remove open_devnull

[PATCH] SELinux: add null device node to selinuxfs, remove open_devnull

This patch adds a null device node to selinuxfs and replaces the SELinux
open_devnull() code by simply acquiring a reference to this node each time,
based on a comment by Al Viro on lkml (see
http://marc.theaimsgroup.com/?l=linux-kernel&m=108664922032035&w=2).

Signed-off-by:  Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by:  James Morris <jmorris@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>