funding+lnwallet: validate ChannelReserve is above DustLimit

This is necessary and is implied by BOLT#02. Both ChannelReserve
parameters should be above both DustLimit parameters. Otherwise,
it is possible for one side to have nothing at stake.

lnwallet/wallet.go

@@ -1266,6 +1266,13 @@ func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) {
 	theirContribution := req.contribution
 	ourContribution := pendingReservation.ourContribution
 
+	// Perform bounds-checking on both ChannelReserve and DustLimit
+	// parameters.
+	if !pendingReservation.validateReserveBounds() {
+		req.err <- fmt.Errorf("invalid reserve and dust bounds")
+		return
+	}
+
 	var (
 		chanPoint *wire.OutPoint
 		err       error
@@ -1564,9 +1571,6 @@ func (l *LightningWallet) handleSingleContribution(req *addSingleContributionMsg
 	pendingReservation.Lock()
 	defer pendingReservation.Unlock()
 
-	// TODO(roasbeef): verify sanity of remote party's parameters, fail if
-	// disagree
-
 	// Validate that the remote's UpfrontShutdownScript is a valid script
 	// if it's set.
 	shutdown := req.contribution.UpfrontShutdown
@@ -1584,6 +1588,14 @@ func (l *LightningWallet) handleSingleContribution(req *addSingleContributionMsg
 	theirContribution := pendingReservation.theirContribution
 	chanState := pendingReservation.partialState
 
+	// Perform bounds checking on both ChannelReserve and DustLimit
+	// parameters. The ChannelReserve may have been changed by the
+	// ChannelAcceptor RPC, so this is necessary.
+	if !pendingReservation.validateReserveBounds() {
+		req.err <- fmt.Errorf("invalid reserve and dust bounds")
+		return
+	}
+
 	// Initialize an empty sha-chain for them, tracking the current pending
 	// revocation hash (we don't yet know the preimage so we can't add it
 	// to the chain).