fix(virtio): fix virtqueue_enable_notify clearing all used_ring flags

The expression `!(uint16_t)VRING_USED_F_NO_NOTIFY` evaluates to 0
(logical NOT of 1), causing `flags &= 0` to clear every flag on the
used ring — not just the intended VRING_USED_F_NO_NOTIFY bit.

Replace with `~(uint16_t)VRING_USED_F_NO_NOTIFY` (bitwise NOT, 0xFFFE)
to only clear the target bit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: agicy

tools/virtio/virtio.c

@@ -441,7 +441,7 @@ void virtqueue_enable_notify(VirtQueue *vq) {
     if (vq->event_idx_enabled) {
         VQ_AVAIL_EVENT(vq) = vq->avail_ring->idx;
     } else {
-        vq->used_ring->flags &= !(uint16_t)VRING_USED_F_NO_NOTIFY;
+        vq->used_ring->flags &= ~(uint16_t)VRING_USED_F_NO_NOTIFY;
     }
     write_barrier();
 }