quic ddd demos: update makefile and demo sources

quic ddd demos: update makefile and demo sources

Update makefile and fix some signedness issues in the demo sources.
Drop stray "\n" in the host-port format string that prevented ddd-01
from working (this was also noticed by Neil H). Also, determine the
length of the message we are sending and send that many bytes (rather
than send sizeof the buffer storing the message).

These changes are part of https://github.com/openssl/project/issues/253

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22542)