MINOR: quic-be: address validation support implementation (RETRY)

MINOR: quic-be: address validation support implementation (RETRY)

- Add ->retry_token and ->retry_token_len new quic_conn struct members to store
  the retry tokens. These objects are allocated by quic_rx_packet_parse() and
  released by quic_conn_release().
- Add <pool_head_quic_retry_token> new pool for these tokens.
- Implement quic_retry_packet_check() to check the integrity tag of these tokens
  upon RETRY packets receipt. quic_tls_generate_retry_integrity_tag() is called
  by this new function. It has been modified to pass the address where the tag
  must be generated
- Add <resend> new parameter to quic_pktns_discard(). This function is called
  to discard the packet number spaces where the already TX packets and frames are
  attached to. <resend> allows the caller to prevent this function to release
  the in flight TX packets/frames. The frames are requeued to be resent.
- Modify quic_rx_pkt_parse() to handle the RETRY packets. What must be done upon
  such packets receipt is:
  - store the retry token,
  - store the new peer SCID as the DCID of the connection. Note that the peer will
    modify again its SCID. This is why this SCID is also stored as the ODCID
    which must be matched with the peer retry_source_connection_id transport parameter,
  - discard the Initial packet number space without flagging it as discarded and
    prevent retransmissions calling qc_set_timer(),
  - modify the TLS cryptographic cipher contexts (RX/TX),
  - wakeup the I/O handler to send new Initial packets asap.
- Modify quic_transport_param_decode() to handle the retry_source_connection_id
  transport parameter as a QUIC client. Then its caller is modified to
  check this transport parameter matches with the SCID sent by the peer with
  the RETRY packet.