Client doesn't read Short packet until handshake completes, so doing
these stuff in one place after handshake is much simpler.

Fix setting remote transport params order

Now server can perform path validation without chaining DCID if a
remote peer does not change DCID as per spec.

Fixes: https://github.com/ngtcp2/ngtcp2/issues/213

Fix typo

Time = 0 is valid time in ngtcp2

so that application is not bothered by another cryptic function.

Still we need to add additional handshake timeout.

Coalesces Initial and Handshake from server on probe.  Include
occasional PING in non-ACK eliciting packets.

Major rework of loss detection mechanism.  It turned out getting it
done is very hard.