Fixes issue eclipse#209.

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

The previous version ignores the option for the local port. That may be
caused by issues using the same default local port for the server and
client.
This enables the use of an specific local port and changes the default
to an ephemeral free port, similar to quite a lot of other UDP clients.
The DEFAULT_PORT is therefore only used for the destination.

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Simple client side implementation indicates support and uses the cid of
the server, when negotiated by that.

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Signed-off-by: Achim Kraus <achim.kraus@cloudcoap.net>

Do not calculate the cookie using the Extensions as these are
different between DTLS1.2 and DTLS1.3

https://datatracker.ietf.org/doc/html/rfc6347#section-4.2.1

When responding to a HelloVerifyRequest, the client MUST use the same
parameter values (version, random, session_id, cipher_suites,
compression_method) as it did in the original ClientHello.  The
server SHOULD use those values to generate its cookie and verify that
they are correct upon cookie receipt.

https://www.rfc-editor.org/rfc/rfc9147.html#section-5.3

The ClientHello up to, but not including the Extensions is the same for
DTLS1.2 and DTLS1.3

Signed-off-by: Jon Shallow <supjps-libcoap@jpshallow.com>

To avoid doxygen warnings regarding outdated configuration options,
this change updates the Doxyfile template to the current version 1.9.8.

Change-Id: Ia60a20e4cb3da375cde48c9ae3ca234200bb8a10