fixes nanomsg#687 POLLHUP is problematic on macOS too...

Basically, we can ignore EV_EOF, as we wind up still alerting
the corresponding events.  EV_ERROR we still treat as HUP.

(The EV_EOF was responsible for prematurely closing the socket
and aborting transactions while there was still data in the socket
buffers.)

src/platform/posix/posix_pollq_kqueue.c

@@ -252,7 +252,7 @@ nni_posix_poll_thr(void *arg)
 				continue;
 			}
 			pf = (void *) ev->udata;
-			if (ev->flags & (EV_ERROR | EV_EOF)) {
+			if (ev->flags & EV_ERROR) {
 				revents |= POLLHUP;
 			}