This patch imports all the definitions for QUIC protocol with few modifications
from 20200720-quic branch of quic-dev repository found at
https://github.com/haproxytech/quic-dev.
We add src/quic_sock.c QUIC specific socket management functions as callbacks
for the control layer: ->accept_conn, ->default_iocb and ->rx_listening.
accept_conn() will have to be defined. The default I/O handler only recvfrom()
the datagrams received. Furthermore, ->rx_listening callback always returns 1 at
this time but should returns 0 when reloading the processus.