MINOR: haterm: enable ktls on the SSL bind line when supported

MINOR: haterm: enable ktls on the SSL bind line when supported

When both USE_LINUX_SPLICE and USE_KTLS are enabled, it's worth
enabling kTLS on the bind line as it significantly increases the
local bit rate as well as through TLS accelerators (up to x2/x3).
The -dT option remains available to disable it. It was verified to
gracefully downgrade when not supported (e.g. OpenSSL 3.0.1 does
this).