ds: do not distinguish between POLLHUP and POLLERR

ds: do not distinguish between POLLHUP and POLLERR

In my experience, both are worthless as any normal read/write
call path will be wanting to check errors and deal with them
appropriately; so we can just call event_read, for now.

Eventually, there'll probably be only one callback for dealing
with all in/out/err/hup events to simplify logic, especially w.r.t
TLS socket negotiation.