Resolve review comments

src/core/lib/iomgr/ev_epoll1_linux.cc

@@ -384,7 +384,11 @@ static void fd_shutdown_internal(grpc_fd* fd, grpc_error* why,
     if (!releasing_fd) {
       shutdown(fd->fd, SHUT_RDWR);
     } else {
-      if (epoll_ctl(g_epoll_set.epfd, EPOLL_CTL_DEL, fd->fd, nullptr) != 0) {
+      /* we need a dummy event for earlier linux versions. */
+      epoll_event dummy_event;
+      memset(&dummy_event, 0, sizeof(dummy_event));
+      if (epoll_ctl(g_epoll_set.epfd, EPOLL_CTL_DEL, fd->fd, &dummy_event) !=
+          0) {
         gpr_log(GPR_ERROR, "epoll_ctl failed: %s", strerror(errno));
       }
     }