MINOR: quic: derive first DCID from client ODCID

MINOR: quic: derive first DCID from client ODCID

Change the generation of the first CID of a connection. It is directly
derived from the client ODCID using a 64-bits hash function. Client
address is added to avoid collision between clients which could use the
same ODCID.

For the moment, this change as no functional impact. However, it will be
directly used for the next commit to be able to remove the ODCID tree.

This should be backported up to 2.7.