Ed25519 signature is incompatible with ndnd

[zjkmxy]

python-ndn/src/ndn/security/signer/ed25519_signer.py

Lines 48 to 52 in bf17383

	h = SHA512.new()
	for blk in contents:
	h.update(blk)
	signer = eddsa.new(self.key, 'rfc8032')
	signature = signer.sign(h)

Passing a pre-hashed content to the library leads to the Ed25519ph variant, which is not used by other NDN libraries.