OpenSSL: Support for kernel TLS offload (KTLS)

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_OPENSSL_KTLS determines if OpenSSL is built with
KTLS support. It defaults to enabled on amd64 and disabled on all
other architectures.

Approved by: re (gjb)
Sponsored by: Netflix

(cherry picked from commit aa906e2a4957db700d9e6cc60857e1afe1aecc85)
(cherry picked from commit c1c52cd57e8810ca294d02220dfa72607c9a5567)