MEDIUM: kqueue: take care of EV_EOF to improve polling status accuracy

MEDIUM: kqueue: take care of EV_EOF to improve polling status accuracy

kevent() always sets EV_EOF with EVFILT_READ to notify of a read shutdown
and EV_EOF with EVFILT_WRITE to notify of a write error. Let's check this
flag to properly update the FD's polled status (FD_POLL_HUP and FD_POLL_ERR
respectively).

It's worth noting that this one can be coupled with a regular read event
to notify about a pending read followed by a shutdown, but for now we only
use this to set the relevant flags (HUP and ERR).

The poller now exhibits the flag HAP_POLL_F_RDHUP to indicate this new
capability.

An improvement may consist in not setting FD_POLL_IN when the "data"
field is null since it normally only reflects the amount of pending
data.