htlcswitch: modify forwarding fee assertion to compare emperical fees

In this commit, we fix a bug that was uncovered by the recent change to
lnwire.MilliSatoshi. Rather than manually compute the diff in fees,
we’ll directly compare the fee that is given against the fee that we
expect.

htlcswitch/link_test.go

@@ -777,7 +777,7 @@ func TestUpdateForwardingPolicy(t *testing.T) {
 		testStartingHeight,
 		n.firstBobChannelLink, n.carolChannelLink)
 
-	// First, send this 1 BTC payment over the three hops, the payment
+	// First, send this 10 mSAT payment over the three hops, the payment
 	// should succeed, and all balances should be updated accordingly.
 	payResp, err := n.makePayment(n.aliceServer, n.carolServer,
 		n.bobServer.PubKey(), hops, amountNoFee, htlcAmt,
@@ -827,7 +827,7 @@ func TestUpdateForwardingPolicy(t *testing.T) {
 	n.firstBobChannelLink.UpdateForwardingPolicy(newPolicy)
 
 	// Next, we'll send the payment again, using the exact same per-hop
-	// payload for each node. This payment should fail as it wont' factor
+	// payload for each node. This payment should fail as it won't factor
 	// in Bob's new fee policy.
 	_, err = n.makePayment(n.aliceServer, n.carolServer,
 		n.bobServer.PubKey(), hops, amountNoFee, htlcAmt,