graph/db: use InboundFee directly from ChannelEdgePolicy

Now that we know that the InboundFee on the ChannelEdgePolicy is always
set appropriately, we can update the GraphCache UpdatePolicy method to
take the InboundFee directly from the ChannelEdgePolicy object.

graph/db/graph_cache.go

@@ -180,17 +180,6 @@ func (c *GraphCache) updateOrAddEdge(node route.Vertex, edge *DirectedChannel) {
 func (c *GraphCache) UpdatePolicy(policy *models.ChannelEdgePolicy, fromNode,
 	toNode route.Vertex, edge1 bool) {
 
-	// Extract inbound fee if possible and available. If there is a decoding
-	// error, ignore this policy.
-	var inboundFee lnwire.Fee
-	_, err := policy.ExtraOpaqueData.ExtractRecords(&inboundFee)
-	if err != nil {
-		log.Errorf("Failed to extract records from edge policy %v: %v",
-			policy.ChannelID, err)
-
-		return
-	}
-
 	c.mtx.Lock()
 	defer c.mtx.Unlock()
 
@@ -216,13 +205,17 @@ func (c *GraphCache) UpdatePolicy(policy *models.ChannelEdgePolicy, fromNode,
 		// policy for node 1.
 		case channel.IsNode1 && edge1:
 			channel.OutPolicySet = true
-			channel.InboundFee = inboundFee
+			policy.InboundFee.WhenSome(func(fee lnwire.Fee) {
+				channel.InboundFee = fee
+			})
 
 		// This is node 2, and it is edge 2, so this is the outgoing
 		// policy for node 2.
 		case !channel.IsNode1 && !edge1:
 			channel.OutPolicySet = true
-			channel.InboundFee = inboundFee
+			policy.InboundFee.WhenSome(func(fee lnwire.Fee) {
+				channel.InboundFee = fee
+			})
 
 		// The other two cases left mean it's the inbound policy for the
 		// node.