[$] Extending in-kernel TLS support

The kernel gained support for the TLSprotocol in the 4.13 release, which came out in September 2017. Thatsupport is incomplete, though, in that it does not provide the kernel witha way to initiate a TLS connection on its own. Instead, user space createsa socket and performs the TLS handshake before handing the socket to thekernel, which can then transfer data using TLS. The situation may be aboutto change as a result of thispatch series from Chuck Lever - though user space will still need toremain in the picture.