This context has the same value attached to it as the context returned
by Session.Context().
In the case of a dialed connection, this context is derived from the
context used for dialing.
The enums have completely different meanings. protocol.PacketType only
defines long header types, whereas logging.PacketType defines all
different types of QUIC packets (including short header packets).
When QUIC abandoned the "stream 0" design, it introduced separate
packet number spaces for packets with different encryption levels.
Packet number compression now also works per packet number space.
The current code doesn't lead to any problems if the peer starts sending
with packet number 0, as we only exchange a few packets in the Initial
and the Handshake packet number space and there's nothing to compress.
It might lead to problems if the peer starts with a large packet number
in one space (which is allowed by the spec), and then starts with a
small packet number in another packet number space.
The RTTStats are used by the logging package. In order to instrument the
congestion package, the RTTStats can't be part of that package any more
(to avoid an import loop).
Duplicate detection uses the same data structure that is used to track
received packets to generate ACK frames. That means that after an old
ACK range has been pruned, a severly delayed packet might be incorrectly
detected as a duplicate.
As we wouldn't have acknowledged receipt of this packet, this situation
would have resulted in a retransmission by the peer anyway, so dropping
the packet won't cause a big regression.
Previously, RunHandshake() would send the session tickets. Now, the
session initiates the sending of the session ticket. This simplifies the
setup a bit, and it will make it possible to include the RTT estimate in
the session ticket without accessing the RTTStats concurrently.
