multi: add experimental endorsement feature bit and disable option

feature/default_sets.go

@@ -96,4 +96,7 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
+	lnwire.ExperimentalEndorsementOptional: {
+		SetNodeAnn: {}, // N
+	},
 }

feature/manager.go

@@ -66,6 +66,10 @@ type Config struct {
 	// NoTaprootOverlay unsets the taproot overlay channel feature bits.
 	NoTaprootOverlay bool
 
+	// NoExperimentalEndorsement unsets any bits that signal support for
+	// forwarding experimental endorsement.
+	NoExperimentalEndorsement bool
+
 	// CustomFeatures is a set of custom features to advertise in each
 	// set.
 	CustomFeatures map[Set][]lnwire.FeatureBit
@@ -199,6 +203,12 @@ func newManager(cfg Config, desc setDesc) (*Manager, error) {
 			raw.Unset(lnwire.SimpleTaprootOverlayChansOptional)
 			raw.Unset(lnwire.SimpleTaprootOverlayChansRequired)
 		}
+
+		if cfg.NoExperimentalEndorsement {
+			raw.Unset(lnwire.ExperimentalEndorsementOptional)
+			raw.Unset(lnwire.ExperimentalEndorsementRequired)
+		}
+
 		for _, custom := range cfg.CustomFeatures[set] {
 			if custom > set.Maximum() {
 				return nil, fmt.Errorf("feature bit: %v "+