event/SocketMonitor: add method Abandon()

src/event/SocketMonitor.cxx

@@ -151,6 +151,19 @@ SocketMonitor::Steal()
 	return result;
 }
 
+void
+SocketMonitor::Abandon()
+{
+	assert(IsDefined());
+
+#ifdef USE_EPOLL
+	fd = -1;
+	loop.Abandon(*this);
+#else
+	Steal();
+#endif
+}
+
 void
 SocketMonitor::Close()
 {