Add ARP to INET or require ND6

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

Hi List

While adding the IN_IFF_TENTATIVE functionality and friends it was pointed out 
that ARP is optional with INET.
The argument at the time being why pay for ARP if there are no real 
interfaces?

However, NS/NA (the ARP equivalent of IPv6) is not optional with INET6, it's 
forced.

So the burning question is this:
Should we turn NS/NA into an option or remove the ARP option?

I'm in favour of the latter as I would find it hard to test patches for the 
former given my restricted hardware set.

Roy