multi: let ForEachChannel be a method on ChannelGraph

Having a `ForEachChannel` method on the `LightningNode` struct itself
results in a `kvdb.Backend` object needing to be stored within the
LightningNode struct. In this commit, this method is replaced with a
`ForEachNodeChannel` method on the `ChannelGraph` struct will perform
the same function without needing the db pointer to be stored within the
LightningNode. This change, the LightningNode struct more closely
represents the schema on disk.

The existing `ForEachNodeChannel` method on `ChannelGraph` is renamed to
`ForEachNodeDirectedChannel`. It performs a slightly different function
since it's call-back operates on Cached policies.

routing/graph.go

@@ -75,7 +75,7 @@ func (g *CachedGraph) Close() error {
 func (g *CachedGraph) forEachNodeChannel(nodePub route.Vertex,
 	cb func(channel *channeldb.DirectedChannel) error) error {
 
-	return g.graph.ForEachNodeChannel(g.tx, nodePub, cb)
+	return g.graph.ForEachNodeDirectedChannel(g.tx, nodePub, cb)
 }
 
 // sourceNode returns the source node of the graph.

routing/router.go

@@ -2824,16 +2824,19 @@ func (r *ChannelRouter) ForEachNode(
 func (r *ChannelRouter) ForAllOutgoingChannels(cb func(kvdb.RTx,
 	*channeldb.ChannelEdgeInfo, *channeldb.ChannelEdgePolicy) error) error {
 
-	return r.selfNode.ForEachChannel(nil, func(tx kvdb.RTx,
-		c *channeldb.ChannelEdgeInfo,
-		e, _ *channeldb.ChannelEdgePolicy) error {
+	return r.cfg.Graph.ForEachNodeChannel(nil, r.selfNode.PubKeyBytes,
+		func(tx kvdb.RTx, c *channeldb.ChannelEdgeInfo,
+			e *channeldb.ChannelEdgePolicy,
+			_ *channeldb.ChannelEdgePolicy) error {
 
-		if e == nil {
-			return fmt.Errorf("channel from self node has no policy")
-		}
+			if e == nil {
+				return fmt.Errorf("channel from self node " +
+					"has no policy")
+			}
 
-		return cb(tx, c, e)
-	})
+			return cb(tx, c, e)
+		},
+	)
 }
 
 // AddProof updates the channel edge info with proof which is needed to