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_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/hex"
 	"testing"
 
+	"github.com/lightningnetwork/lnd/fn/v2"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/routing/route"
@@ -37,11 +38,17 @@ func TestGraphCacheAddNode(t *testing.T) {
 			channelFlagA, channelFlagB = 1, 0
 		}
 
+		inboundFee := lnwire.Fee{
+			BaseFee: 10,
+			FeeRate: 20,
+		}
+
 		outPolicy1 := &models.ChannelEdgePolicy{
 			ChannelID:    1000,
 			ChannelFlags: lnwire.ChanUpdateChanFlags(channelFlagA),
 			ToNode:       nodeB,
 			// Define an inbound fee.
+			InboundFee: fn.Some(inboundFee),
 			ExtraOpaqueData: []byte{
 				253, 217, 3, 8, 0, 0, 0, 10, 0, 0, 0, 20,
 			},