[e2e] Legal fragment sizes

[Bob Braden]

  *> 
  *> I expect that most people will have also assumed that the maximum legal
  *> payload is 64K, and their code probably reflects it - i.e. they may be
  *> calculating the payload size in a 16-bit variable, they may have a maximum
  *> buffer size of 64K, etc. So many (most?) implementations won't work with a
  *> payload of more than 64K.
  *> 
  *> 	Noel
  *> 

I wonder how many stacks we can crash this way!?

Bob Braden