[ofw] udapl for windows

[Sean Hefty]

>Is there any reason why the windows implementation will not use Arp for
>the
>IP -> GID mapping?
>
>This code looks trivial.

Eventually IB routers will exist, and we'll have to deal with multiple IP
subnets, which will require a different solution than ARP.

That said, short term, I don't know how trivial it is to get to this data.  (I
haven't looked at the OFW code, and it's been years since I've written any
Windows kernel code.)  My understanding is that ipoib hides the actual GID
addresses from the rest of the Windows stack.  So even if an interface exists in
Windows for getting the MAC address, I don't know if it's usable for our
purposes, or if we need a direct interface into ipoib.

- Sean