lnwallet: only the initiator needs to validate new fee updates

In this commit, we fix an existing bug, as only the initiator needs to
validate any new fee updates. If the initiator sends an invalid fee,
then it will be rejected by the responder as it may put them below
their required reserve.

lnwallet/channel_test.go

@@ -3385,7 +3385,7 @@ func TestFeeUpdateRejectInsaneFee(t *testing.T) {
 	// Create a test channel which will be used for the duration of this
 	// unittest. The channel will be funded evenly with Alice having 5 BTC,
 	// and Bob having 5 BTC.
-	aliceChannel, bobChannel, cleanUp, err := createTestChannels(1)
+	aliceChannel, _, cleanUp, err := createTestChannels(1)
 	if err != nil {
 		t.Fatalf("unable to create test channels: %v", err)
 	}
@@ -3401,9 +3401,6 @@ func TestFeeUpdateRejectInsaneFee(t *testing.T) {
 	if err := aliceChannel.UpdateFee(newFeeRate); err == nil {
 		t.Fatalf("alice should've rejected fee update")
 	}
-	if err := bobChannel.ReceiveUpdateFee(newFeeRate); err == nil {
-		t.Fatalf("bob should've rejected fee update")
-	}
 }
 
 // TestChannelRetransmissionFeeUpdate tests that the initiator will include any