[e2e] TCP Framing

[Erik Nordmark]

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.

   Erik