OpenSSL ephemeral key behaviour changed in 1.1.0

[daurnimator]

Since OpenSSL 1.1.1, setting the ephemeral key to an EC key only sets the supported EC groups list. As we set prime256v1 unconditionally, this breaks interop with servers that don't support prime256v1.

[daurnimator]

The solution is to try and call :setGroups rather than :setEphemeralKey.