Fix iomux_update_events(), it didn't actually update the events !

src/iomux_impl.c

@@ -149,6 +149,7 @@ int iomux_update_events(struct IOMux *mux, struct IOMuxFD *fd, unsigned int what
     assert(fd->fd >= 0);
     
     if (fd->what != what) {
+        fd->what = what;
         rc = mux->ops.update_events_impl(mux, fd);
     }