[e2e] TCP Framing

[Allison Mankin]

> As much as we might dislike the various middle boxes,
> I wonder what would happen if one of these TCP connections
> passed through a middle box. While many middleboxes tweak things
> on a packet by packet basis, there might be some that are essentially
> implemented as a read+write loop in application space, i.e.
> the TCP segment boundaries would not be preserved.
> 
> Thus trying to make the TCP segment boundaries matter for the ULP
> is threading into unchartered territory.

The shim does have a provision for detecting that middleboxes have
happened to it (resegmenting) and reverting to normal processing if so.

Reviewing to see that detection is a s sure as the designers hope would
be good.

Allison