routing/pathfind: pass ignore disable flags for local channels

To decouple our own path finding from the graph state, we don't consider
the disable bit when attempting to use local channels. Instead the
bandwidth hints will be zero for local inactive channels.

We alos modify the unit test to check that the disable flag is ignored
for local edges.

routing/pathfind.go

@@ -462,7 +462,11 @@ type graphParams struct {
 
 	// bandwidthHints is an optional map from channels to bandwidths that
 	// can be populated if the caller has a better estimate of the current
-	// channel bandwidth than what is found in the graph.
+	// channel bandwidth than what is found in the graph. If set, it will
+	// override the capacities and disabled flags found in the graph for
+	// local channels when doing path finding. In particular, it should be
+	// set to the current available sending bandwidth for active local
+	// channels, and 0 for inactive channels.
 	bandwidthHints map[uint64]lnwire.MilliSatoshi
 }
 
@@ -585,10 +589,15 @@ func findPath(g *graphParams, r *restrictParams,
 
 		fromVertex := Vertex(fromNode.PubKeyBytes)
 
-		// If the edge is currently disabled, then we'll stop here, as
-		// we shouldn't attempt to route through it.
+		// If this is not a local channel and it is disabled, we will
+		// skip it.
+		// TODO(halseth): also ignore disable flags for non-local
+		// channels if bandwidth hint is set?
+		isSourceChan := fromVertex == sourceVertex
 		edgeFlags := lnwire.ChanUpdateFlag(edge.Flags)
-		if edgeFlags&lnwire.ChanUpdateDisabled != 0 {
+		isDisabled := edgeFlags&lnwire.ChanUpdateDisabled != 0
+
+		if !isSourceChan && isDisabled {
 			return
 		}