Add a secctx_to_secid() LSM hook to go along with the existing
secid_to_secctx() LSM hook.  This patch also includes the SELinux
implementation for this hook.
Signed-off-by: NPaul Moore <paul.moore@hp.com>
Acked-by: NStephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: NJames Morris <jmorris@namei.org>