Consider initial connection phase for public networks:
* simultaneous connections to seeds
* very quick handshakes
* got five handshaked peers and some getaddr requests sent
* but addr replies won't trigger new connections
* so we can stay with just five connections until any of them breaks or a
(long) address checking timer fires
This new timers solves the problem, it's adaptive at the same time. If we have
enough peers we won't be waking up often.
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