From: Pavel Emelyanov <xemul@openvz.org>
Date: Thu, 10 Jan 2008 18:05:25 +0300

> When I studied the neighbor code I puzzled over what
> the NUD can mean for quite a long time.
> 
> Finally I asked Alexey and he said that this was smth
> like "neighbor unreachability detection".
> 
> Does it worth adding a comment helping future developers 
> understand what's going on?
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

NUD is a common acronym in the IPV6 RFCs and various books
on the topic, but it doesn't hurt to add this comment so I
applied this patch thanks.