multi: add option to disable route blinding, rejecting at link

Add an option to disable route blinding, failing back any HTLC with
a blinding point set when we haven't got the feature enabled.

Note that this commit only handles the case where we're chosen as the
relaying node (where the blinding point is in update_add_htlc), we'll
add handling for the introduction node case once we get to handling of
blinded payloads).

lncfg/protocol.go

@@ -54,6 +54,9 @@ type ProtocolOptions struct {
 	// also mean that we won't respond with timestamps if requested by our
 	// peers.
 	NoTimestampQueryOption bool `long:"no-timestamp-query-option" description:"do not query syncing peers for announcement timestamps and do not respond with timestamps if requested"`
+
+	// NoRouteBlindingOption disables forwarding of payments in blinded routes.
+	NoRouteBlindingOption bool `long:"no-route-blinding" description:"do not forward payments that are a part of a blinded route"`
 }
 
 // Wumbo returns true if lnd should permit the creation and acceptance of wumbo
@@ -97,3 +100,8 @@ func (l *ProtocolOptions) NoAnySegwit() bool {
 func (l *ProtocolOptions) NoTimestampsQuery() bool {
 	return l.NoTimestampQueryOption
 }
+
+// NoRouteBlinding returns true if forwarding of blinded payments is disabled.
+func (l *ProtocolOptions) NoRouteBlinding() bool {
+	return l.NoRouteBlindingOption
+}

lncfg/protocol_integration.go

@@ -57,6 +57,9 @@ type ProtocolOptions struct {
 	// also mean that we won't respond with timestamps if requested by our
 	// peers.
 	NoTimestampQueryOption bool `long:"no-timestamp-query-option" description:"do not query syncing peers for announcement timestamps and do not respond with timestamps if requested"`
+
+	// NoRouteBlindingOption disables forwarding of payments in blinded routes.
+	NoRouteBlindingOption bool `long:"no-route-blinding" description:"do not forward payments that are a part of a blinded route"`
 }
 
 // Wumbo returns true if lnd should permit the creation and acceptance of wumbo
@@ -92,3 +95,8 @@ func (l *ProtocolOptions) ZeroConf() bool {
 func (l *ProtocolOptions) NoAnySegwit() bool {
 	return l.NoOptionAnySegwit
 }
+
+// NoRouteBlinding returns true if forwarding of blinded payments is disabled.
+func (l *ProtocolOptions) NoRouteBlinding() bool {
+	return l.NoRouteBlindingOption
+}