lnwallet+htlcswitch: add NewCommitState struct, modify send/recv sig to accept

In this commit, we add a new NewCommitState struct. This preps us for
the future change wherein a partial signature is also added to the mix.
All related tests and type signatures have also been updated
accordingly.

htlcswitch/link.go

@@ -1899,7 +1899,10 @@ func (l *channelLink) handleUpstreamMsg(msg lnwire.Message) {
 		// We just received a new updates to our local commitment
 		// chain, validate this new commitment, closing the link if
 		// invalid.
-		err = l.channel.ReceiveNewCommitment(msg.CommitSig, msg.HtlcSigs)
+		err = l.channel.ReceiveNewCommitment(&lnwallet.CommitSigs{
+			CommitSig:  msg.CommitSig,
+			HtlcSigs:   msg.HtlcSigs,
+		})
 		if err != nil {
 			// If we were unable to reconstruct their proposed
 			// commitment, then we'll examine the type of error. If
@@ -2215,7 +2218,7 @@ func (l *channelLink) updateCommitTx() error {
 		return nil
 	}
 
-	theirCommitSig, htlcSigs, pendingHTLCs, err := l.channel.SignNextCommitment()
+	newCommit, err := l.channel.SignNextCommitment()
 	if err == lnwallet.ErrNoWindow {
 		l.cfg.PendingCommitTicker.Resume()
 		l.log.Trace("PendingCommitTicker resumed")
@@ -2247,7 +2250,7 @@ func (l *channelLink) updateCommitTx() error {
 	// pending).
 	newUpdate := &contractcourt.ContractUpdate{
 		HtlcKey: contractcourt.RemotePendingHtlcSet,
-		Htlcs:   pendingHTLCs,
+		Htlcs:   newCommit.PendingHTLCs,
 	}
 	err = l.cfg.NotifyContractUpdate(newUpdate)
 	if err != nil {
@@ -2262,9 +2265,9 @@ func (l *channelLink) updateCommitTx() error {
 	}
 
 	commitSig := &lnwire.CommitSig{
-		ChanID:    l.ChanID(),
-		CommitSig: theirCommitSig,
-		HtlcSigs:  htlcSigs,
+		ChanID:     l.ChanID(),
+		CommitSig:  newCommit.CommitSig,
+		HtlcSigs:   newCommit.HtlcSigs,
 	}
 	l.cfg.Peer.SendMessage(false, commitSig)