This patch updates the auto-generated code to match the latest tooling
versions.
In particular, the protobufs are regenerated, and the new version no
longer supports unkeyed literals, so some minor changes are needed.
Other than that, the cipher list is extended with the latest ciphers.
There are a couple of places where it's handy to print TLS constants in
human-readable form.
To do so, we need functions that take TLS constants (usually in uint16 form)
and give us friendly strings.
Go's crypto/tls package does not provide us with this, so this patch
introduces a new module with that purpose.
