This merges upstream patches from OpenSSL's master branch to add
KTLS infrastructure for TLS 1.0-1.3 including both RX and TX
offload and SSL_sendfile support on both Linux and FreeBSD.
Note that TLS 1.3 only supports TX offload.
A new WITH/WITHOUT_KTLS determines if OpenSSL is built with KTLS
support. It defaults to enabled.