net: tun: stop NAPI when detaching queues

While looking at a syzbot report I noticed the NAPI only gets
disabled before it's deleted. I think that user can detach
the queue before destroying the device and the NAPI will never
be stopped.

Fixes: 94317099

 ("tun: enable NAPI for TUN/TAP driver")
Acked-by: Petar Penkov <ppenkov@aviatrix.com>
Link: https://lore.kernel.org/r/20220623042105.2274812-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>