event/TimerEvent: use base_hook instead of member_hook

src/event/Loop.hxx

@@ -66,9 +66,7 @@ class EventLoop final : SocketMonitor
 
 	using TimerSet =
 		boost::intrusive::multiset<TimerEvent,
-					   boost::intrusive::member_hook<TimerEvent,
-									 TimerEvent::TimerSetHook,
-									 &TimerEvent::timer_set_hook>,
+					   boost::intrusive::base_hook<boost::intrusive::set_base_hook<>>,
 					   boost::intrusive::compare<TimerCompare>,
 					   boost::intrusive::constant_time_size<false>>;
 	TimerSet timers;

src/event/TimerEvent.hxx

@@ -36,12 +36,11 @@ class EventLoop;
  * thread that runs the #EventLoop, except where explicitly documented
  * as thread-safe.
  */
-class TimerEvent final {
+class TimerEvent final
+	: public boost::intrusive::set_base_hook<>
+{
 	friend class EventLoop;
 
-	typedef boost::intrusive::set_member_hook<> TimerSetHook;
-	TimerSetHook timer_set_hook;
-
 	EventLoop &loop;
 
 	typedef BoundMethod<void() noexcept> Callback;
@@ -67,7 +66,7 @@ public:
 	}
 
 	bool IsActive() const noexcept {
-		return timer_set_hook.is_linked();
+		return is_linked();
 	}
 
 	void Schedule(std::chrono::steady_clock::duration d) noexcept;