[net2-wg] link estimator interface

[Joe Polastre]

> Without absolute values, it would be difficult to do
> blacklisting. That is a real example.

Why not?  I can blacklist nodes based on their relative performance. 
I'd actually rather do that than completely write them off--for all
the uses that I've seen, I only care about who can get my message
through relative to everyone else.  Still not convinced there is a
real need for absolute values.

Just as an FYI, we went through this same exercise when we were
working on SP, but for the priority mechanism.  Initially, there were
suggestions of having absolute latency bounds, deadlines, and multiple
priority levels.  We ended up settling on the easiest, and so far most
useful abstraction--a single bit that prioritizes messages relative to
the other ones in the pool.

-Joe