block/nbd: connect_thread_func(): do qio_channel_set_delay(false)

nbd_open() does it (through nbd_establish_connection()).
Actually we lost that call on reconnect path in 1dc4718
"block/nbd: use non-blocking connect: fix vm hang on connect()"
when we have introduced reconnect thread.

Fixes: 1dc4718
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210610100802.5888-5-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/nbd.c

@@ -408,6 +408,8 @@ static void *connect_thread_func(void *opaque)
         thr->sioc = NULL;
     }
 
+    qio_channel_set_delay(QIO_CHANNEL(thr->sioc), false);
+
     qemu_mutex_lock(&thr->mutex);
 
     switch (thr->state) {