Only restore ed key clamping if key was imported

[ColtonWilley]

Libssh2 generates and then exports a curve25519 private key. If we generated the key, we are incorrectly clamping the private key with zero values on export. Fix to only clamp if key was imported.

[padelsbach]

ecx->hasPriv is checked for private keys around like 793. Should ecx->clamped be checked there as well?

Edit: I believe not since this key may have been generated, and thus not clamped.

[ColtonWilley]

ecx->hasPriv is checked for private keys around like 793. Should ecx->clamped be checked there as well?

I dont think so. Whether it has an underlying private key is independent of clamping.

[padelsbach]

ecx->hasPriv is checked for private keys around like 793. Should ecx->clamped be checked there as well?

Edit: I believe not since this key may have been generated, and thus not clamped.

In any case, it might be good to add a comment that the clamped flag is specifically for imported and not generated keys