selinux: Set the peer label correctly on connected UNIX domain sockets

Correct a problem where we weren't setting the peer label correctly on
the client end of a pair of connected UNIX sockets.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>