Why the check to make sure that one doesn't shrink the number
of vnodes?  Difficult to implement the shrinking?

	Sean. (full of questions today, aren't i?)

        case KERN_MAXVNODES:
                old_vnodes = desiredvnodes;
                error = sysctl_int(oldp, oldlenp, newp, newlen, &desiredvnodes);
                if (old_vnodes > desiredvnodes) {
                        desiredvnodes = old_vnodes;
                        return (EINVAL);
                }
                return (error);