[PATCH] selinux: tracer SID fix

Fix SELinux to not reset the tracer SID when the child is already being
traced, since selinux_ptrace is also called by proc for access checking
outside of the context of a ptrace attach.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>