BUG/MEDIUM: quic: avoid freezing 0RTT connections

BUG/MEDIUM: quic: avoid freezing 0RTT connections

This issue came with this commit:

	f627b92 BUG/MEDIUM: quic: always validate sender address on 0-RTT

and could be easily reproduced with picoquic QUIC client with -Q option
which splits a big ClientHello TLS message into two Initial datagrams.
A second condition must be fulfilled to reprodue this issue: picoquic
must not send the token provided by haproxy (NEW_TOKEN). To do that,
haproxy must be patched to prevent it to send such tokens.

Under these conditions, if haproxy has enough time to reply to the first Initial
datagrams, when it receives the second Initial datagram it sends a Retry paquet.
Then the client ignores the Retry paquet as mentionned by RFC 9000:

 17.2.5.2. Handling a Retry Packet
    A client MUST accept and process at most one Retry packet for each connection
    attempt. After the client has received and processed an Initial or Retry packet
    from the server, it MUST discard any subsequent Retry packets that it receives.

On its side, haproxy has closed the connection. When it receives the second
Initial datagram, it open a new connection but with Initial packets it
cannot decrypt (wrong ODCID) leaving the client without response.

To fix this, as the aim of the token (NEW_TOKEN) sent by haproxy is to validate
the peer address, in place of closing the connection when no token was received
for a 0RTT connection, one leaves this validation to the handshake process.
Indeed, the peer adress is validated during the handshake when a valid handshake
packet is received by the listener. But as one does not want haproxy to process
0RTT data when no token was received, one does not accept the connection before
the successful handshake completion. In addition to this, the 0RTT packets
are not released after successful handshake completion when no token was received
to leave a chance to haproxy to process these 0RTT data in such case (see
quic_conn_io_cb()).

Must be backported as far as 2.9.

(cherry picked from commit b1af5dabf0c4af1eda3a520a90332df1f4c12dcf)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>