wire: Zero out secrets signature for commitment hash

The signature changes depending on the published previous RS message hashes,
and therefore cannot be used to create the commitment hash covering the actual
secrets being published by the message.

wire/msgmixsecrets.go

@@ -202,6 +202,7 @@ func (msg *MsgMixSecrets) Hash() chainhash.Hash {
 // messages.
 func (msg *MsgMixSecrets) Commitment(h hash.Hash) chainhash.Hash {
 	msgCopy := *msg
+	msgCopy.Signature = [64]byte{}
 	msgCopy.SeenSecrets = nil
 	msgCopy.WriteHash(h)
 	return msgCopy.hash