apps/s_server: Add ktls option

apps/s_server: Add ktls option

From openssl-3.0.0-alpha15, KTLS is turned off by default, even if
KTLS feature in compilation, which makes it difficult to use KTLS
through s_server/s_client, so a parameter option 'ktls' is added
to enable KTLS through cmdline.

At the same time, SSL_sendfile() depends on KTLS feature to work
properly, make parameters sendfile depend on parameters ktls.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Reviewed-by: Paul Yang <kaishen.yy@antfin.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16609)