virtio_net: disable premapped mode by default

virtio_net: disable premapped mode by default

Now, the premapped mode encounters some problem.

    http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com

So we disable the premapped mode by default.
We can re-enable it in the future.

Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
Reported-by: "Si-Wei Liu" <si-wei.liu@oracle.com>
Closes: http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540c0a@oracle.com
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Takero Funaki <flintglass@gmail.com>
Link: https://patch.msgid.link/20240906123137.108741-4-xuanzhuo@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>