OpenSSL: Refactor KTLS tests to better support TLS 1.3.

Most of this upstream commit touched tests not included in the
vendor import. The one change merged in is to remove a constant
only present in an internal header to appease the older tests.

Reviewed by: jkim
Obtained from: OpenSSL (e1fdd5262e4a45ce3aaa631768e877ee7b6da21b)
MFC after: 5 days
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D31442