selinux: Permit bounded transitions under NO_NEW_PRIVS or NOSUID.

If the callee SID is bounded by the caller SID, then allowing
the transition to occur poses no risk of privilege escalation and we can
therefore safely allow the transition to occur.  Add this exemption
for both the case where a transition was explicitly requested by the
application and the case where an automatic transition is defined in
policy.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Paul Moore <pmoore@redhat.com>