Fix EV_CLOSED detection/reporting (epoll only)

Fix EV_CLOSED detection/reporting (epoll only)

- EV_CLOSED is EPOLLRDHUP in epoll
- EPOLLRDHUP reported w/o EPOLLHUP if the socket closed with shutdown(SHUT_WR)
- EPOLLRDHUP reported w/  EPOLLHUP if the socket closed with close()
  so in this case epoll backend will detect this event as error
  (EV_READ|EV_WRITE), since the epoll_ctl() will return EPOLLRDHUP with
  EPOLLHUP set, but this is not correct, let's fix this.

Fixes: #984