Respect a requested PortalIP if possible

This will make DNS possible on a static IP.
Eh, leave it, we'll need it for authz

----- Original Message -----
> > @@ -224,8 +232,10 @@ func (rs *REST) Update(ctx api.Context, obj
> > runtime.Object) (<-chan runtime.Obje
> >  		if err != nil {
> >  			return nil, err
> >  		}
> > +		if service.PortalIP != cur.PortalIP {
> > +			return nil, errors.NewForbidden("service", service.Name, "PortalIP is
> > immutable")
> 
> Fair enough.  I can change this - get rid of NewForbidden entirely?
> 
> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/GoogleCloudPlatform/kubernetes/pull/1982/files#r19351418