In selinux_netlbl_skbuff_setsid() we leverage a cached NetLabel
secattr whenever possible.  However, we never check to ensure that
the desired SID matches the cached NetLabel secattr.  This patch
checks the SID against the secattr before use and only uses the
cached secattr when the SID values match.
Signed-off-by: Paul Moore <pmoore@redhat.com>