ACK frame largest_ack field is always the largest packet number even
if the ACK that contains largest_ack has been acknowledged by a remote
endpoint.

Deal with initial_scid, retry_scid, and original_dcid.  We need to set
and get QUIC transport parameters timely manner.  Therefore, transport
parameter operations are now done by ngtcp2_crypto library.
Applications do not need to do set it manually.  Added several
callback function implementations to ngtcp2_crypto library which can
be directly passed to ngtcp2_callbacks: client_initial, recv_retry,
and recv_client_initial.  Installation of initial packet number space
encryption keys is now handled by ngtcp2_crypto library.  They are
done in ngtcp2_crypto_client_initial_cb, ngtcp2_crypto_recv_retry_cb
and ngtcp2_crypto_recv_client_initial_cb.

Time = 0 is valid time in ngtcp2

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

It now defaults to 2 and includes CID exchanged during handshake.

https://tools.ietf.org/html/draft-cheng-iccrg-delivery-rate-estimation-00