Review: Fix regression that did not allow "route change" that didn't re-specify the gateway

[Mike Karels]

> > A change a while back (r264986) broke the ability to change a route's
> > parameters if the gateway wasn't explicitly specified again.  For

> Was the a feature by accident or design?  As the man page does not
> say that "gateway" is optional on a change command, it shows it
> as a required parameter.

I can confirm that the feature was by design, and it has been that way
for a long time.  The man page wasn't sufficiently clear about the
difference between "change" and "add" (or, for that matter, "get",
which does not require the gateway either, for obvious reasons).

I'll take a look at the review.

		Mike