Remove Initial Value for vq->info.notify_off in virtio-net

This commit removes the initialization of vq->info.notify_off
value in the virtio-net implementation. The reason for this
change is that during the execution of RX and TX enable
callback functions, the `vm_ioeventfd_register` function
registers the ioeventfd at the same address repeatly.
Therefore, the notify_off value is now initialized directly
within the virtqueue enable callback functions.

Author: jimmylu890303

src/virtq.c

@@ -25,7 +25,6 @@ void virtq_disable(struct virtq *vq) {}
 void virtq_init(struct virtq *vq, void *dev, struct virtq_ops *ops)
 {
     vq->info.size = VIRTQ_SIZE;
-    vq->info.notify_off = 0;
     vq->info.enable = 0;
     vq->next_avail_idx = 0;
     vq->used_wrap_count = 1;