The test establish a TLS connection on a socketpair, and then
check that by injecting arbitrary data in the client we receive
the exact same thing on the server side.
The test need more sophistication in general, as to arbitrarily test
TLS versions, different ciphers & key exchange, certificates, etc.
the API stays mostly similar except for clientkeyxchg that need a bytes instead of [word8].
remove lots of unnessary packing/unpacking when setting up ciphers.
