QUIC proxy works like kcp proxy, it can proxy TCP streams and transfer data with QUIC.
QUIC has better congestion algorithm (BBR) for network with both high loss rate and high bandwidth.
QUIC proxy can be enabled by passing `--enable-quic-proxy` to easytier in the client side. The proxy status can be viewed by `easytier-cli proxy`.
This patch implements:
1. A dns server that handles .et.net. zone in local and forward all other queries to system dns server.
2. A dns server instance which is a singleton in one machine, using one specific tcp port to be exclusive with each other. this instance is responsible for config system dns and run the dns server to handle dns queries.
3. A dns client instance that all easytier instance will run one, this instance will try to connect to dns server instance, and update the dns record in the dns server instance.
this pr only implements the system config for windows. linux & mac will do later.
if smoltcp bind only once on tcp socket, it can only accept exactly
one syn packet in one round. other syn packets will be dropped and
client will receive a RST packet.
DavHau