Improve debugging.
Delay SRTT when no response come.
Debugging.
Update addresses.h.

Mostly imported from the other branch, without the v4-mapped
extensions.
Fix: SRTT when no response come.
Fix some logging.
Fix: don't try to set v4 option on v6 socket.
Fix: use a constructor, because this will set some fields.

In this case, the "addrlen" field.
Fix bug: set the right ID and seqno in sent packets.
More uniform logging, for easier awk parsing + seq indications.
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