[ofa-general] removing PR caching from IPoIB

[Sean Hefty]

> There are some packets that are sent with no neighbour structure;
> unicast ARPs are the case that I know of, although I'm not positive
> there aren't other such cases.  See unicast_arp_send() in the IPoIB
> source for details.

My first thought was to tie the IPoIB PR lifetime to ipoib_neigh and 
treat unicast ARPs separately.  For unicast ARPs, I was thinking of 
setting the skb as the context of the PR query and send it after it 
completed, but I hadn't considered cleanup.

As an alternate approach, I could try adding a reference count to 
ipoib_path that's incremented once for each neighbour or when sending a 
unicast ARP.  This may be equivalent to merging ipoib_ah and ipoib_path, 
but I haven't looked at the details of trying this.

Do you have a preference or any other suggestions that would limit the 
PR lifetime?

- Sean