All ECDH keys are silently created using P-256

[gnarea]

I think this is a bug in PKI.js or, perhaps more likely, node-webcrypto-ossl. This can be reproduced by calling generateECDHKeyPair with a curve other than P-256.

This isn't a major issue because support for P-256 is required and support for the other curves is just recommended.

Once this is fixed, reinstate this commented-out test:

https://github.com/relaycorp/relaydev/blob/master/functional_tests/test-key-genecdh.sh#L5-L8