Fix checks for whether X25519 and X448 are supported

[dcooper16]

Describe your changes

In some cases OpenSSL returns an "unsupported" message rather than a "not found" message if X25519 and X448 are not supported. This PR changes the check for whether X5519 and X448 are supported for checking for either response.

This happened for me with the distribution version of OpenSSL. I am getting the following response:

> /usr/bin/openssl genpkey -algorithm X25519
Error initializing X25519 context
40373E1D627F0000:error:0308010C:digital envelope routines:inner_evp_generic_fetch:unsupported:../crypto/evp/evp_fetch.c:349:Global default library context, Algorithm (X25519 : 110), Properties (<null>)

What is your pull request about?

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Typo fix
• Documentation update
• Update of other files

If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs and the indentation is five spaces
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
• If it's a bigger change: I added myself to CREDITS.md (alphabetical order) and the change to CHANGELOG.md

[drwetter]

Thanks, David!

Don't we need a backport for this., too?