virtio_net: support tx queue resize

This patch implements the resize function of the tx queues.
Based on this function, it is possible to modify the ring num of the
queue.

Inludes fixup:

virtio_net: fix for stuck when change tx ring size with dev down

When dev is set to DOWN state, napi has been disabled, if we modify the
ring size at this time, we should not call napi_disable() again, which
will cause stuck.

And all operations are under the protection of rtnl_lock, so there is no
need to consider concurrency issues.

Message-Id: <20220801063902.129329-42-xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220811080258.79398-3-xuanzhuo@linux.alibaba.com>
Reported-by: Kangjie Xu <kangjie.xu@linux.alibaba.com>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>