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.

routing/pathfind_test.go

@@ -666,15 +666,25 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 			return nil, err
 		}
 
-		getExtraData := func(
-			end *testChannelEnd) lnwire.ExtraOpaqueData {
+		getInboundFees := func(
+			end *testChannelEnd) fn.Option[lnwire.Fee] {
 
-			var extraData lnwire.ExtraOpaqueData
 			inboundFee := lnwire.Fee{
 				BaseFee: int32(end.InboundFeeBaseMsat),
 				FeeRate: int32(end.InboundFeeRate),
 			}
-			require.NoError(t, extraData.PackRecords(&inboundFee))
+
+			return fn.Some(inboundFee)
+		}
+		getExtraData := func(
+			end *testChannelEnd) lnwire.ExtraOpaqueData {
+
+			var extraData lnwire.ExtraOpaqueData
+
+			inboundFee := getInboundFees(end)
+			inboundFee.WhenSome(func(fee lnwire.Fee) {
+				require.NoError(t, extraData.PackRecords(&fee))
+			})
 
 			return extraData
 		}
@@ -701,6 +711,7 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 				FeeBaseMSat:               node1.FeeBaseMsat,
 				FeeProportionalMillionths: node1.FeeRate,
 				ToNode:                    node2Vertex,
+				InboundFee:                getInboundFees(node1), //nolint:ll
 				ExtraOpaqueData:           getExtraData(node1),
 			}
 			if err := graph.UpdateEdgePolicy(edgePolicy); err != nil {
@@ -731,6 +742,7 @@ func createTestGraphFromChannels(t *testing.T, useCache bool,
 				FeeBaseMSat:               node2.FeeBaseMsat,
 				FeeProportionalMillionths: node2.FeeRate,
 				ToNode:                    node1Vertex,
+				InboundFee:                getInboundFees(node2), //nolint:ll
 				ExtraOpaqueData:           getExtraData(node2),
 			}
 			if err := graph.UpdateEdgePolicy(edgePolicy); err != nil {