iqnets: opportunistic XYZ, e.g. "begin xmit"

[Zenaan Harkness]

>     - B checks its current link undertakings (bulk, r/t, total b/w vs
>       b/w availability etc), and offers to A something like:
> 
>       - I can ACK your request not before 13 minutes, (presumably due
>         to current link contracts);
> 
>         I will hold open this offer for you, for 10 seconds, i.e. I
>         will not enter new link contracts before $NOW + 10s.

Such protocols lead to information exposure (i.e. privacy bugs),
since if stalker node S "the snake" makes a request of node B during
this 10s window, and gets an "unusual response latency", then S can
gather than B may be holding back additional contracts due to the
above phone call "headroom link" proto.

This may not be a lot of information, and may ultimately not be
useful ("exploitable"), but we must keep such "protocol level"
exposures in mind.

If there are various reasons, including say "arbitrarily random"
request-response latency occurrences, we may either mitigate, or
completely eliminate, such information exposures.