lnwire: add update_fee message type.

lnwire/lnwire_test.go

@@ -523,6 +523,12 @@ func TestLightningWireProtocol(t *testing.T) {
 				return mainScenario(&m)
 			},
 		},
+		{
+			msgType: MsgUpdateFee,
+			scenario: func(m UpdateFee) bool {
+				return mainScenario(&m)
+			},
+		},
 		{
 			msgType: MsgChannelAnnouncement,
 			scenario: func(m ChannelAnnouncement) bool {