Applying the inet6 ND state engine to inet4

[Roy Marples <roy%marples.name@localhost>]

One of the really nice things about INET6 is Neighbour Discovery. Not really the 
on-wire protocol itself, but the state engine it has. The equivalent in ARP is 
not quite so nice.

I think it would be a good win to split the ND state engine out of netinet6 and 
into net to make it protocol agnostic (which it already is to some extent thanks 
the the LLE work done prior).

Why is this a good win? Well, the ARP state relies on the net.inet.arp.keep 
timer of 20 minutes where it thinks that once resolved the host *will* be up for 
20 minutes. ND on the other hand sets short timers based on the flow of data so 
we can readily detect hosts becoming unreachable a lot faster.

Thoughts?

Roy