routing: restore in memory selfNode within the ChannelRouter

In this commit we restore the in memory ChannelRouter as we’ll no
dynamically set the ChannelRouter’s pointer within he spec path finding
test example.

routing/pathfind_test.go

@@ -718,6 +718,7 @@ func TestPathFindSpecExample(t *testing.T) {
 	if err := ctx.graph.SetSourceNode(aliceNode); err != nil {
 		t.Fatalf("unable to set source node: %v", err)
 	}
+	ctx.router.selfNode = aliceNode
 	source, err := ctx.graph.SourceNode()
 	if err != nil {
 		t.Fatalf("unable to retrieve source node: %v", err)