lnwallet+lnd: ensure curve parameters are set to avoid panics

This commit fixes a bug introduced by the past attempt to Make Logging
Great Again. Since we unset the curve parameters when reading/writing
the messages, if we have a lingering reference that’s active elsewhere
in the daemon, then we’ll modify that reference. To fix this, we now
explicitly set the Curve parameters in two areas.

A similar commit has been pushed to lightning-onion.

lnwallet/channel.go

@@ -1312,6 +1312,7 @@ func (lc *LightningChannel) ReceiveNewCommitment(rawSig []byte,
 
 	// Ensure that the newly constructed commitment state has a valid
 	// signature.
+	theirMultiSigKey.Curve = btcec.S256()
 	sig, err := btcec.ParseSignature(rawSig, btcec.S256())
 	if err != nil {
 		return err

server.go

@@ -90,6 +90,7 @@ func newServer(listenAddrs []string, notifier chainntnfs.ChainNotifier,
 	if err != nil {
 		return nil, err
 	}
+	privKey.Curve = btcec.S256()
 
 	listeners := make([]net.Listener, len(listenAddrs))
 	for i, addr := range listenAddrs {