net: tun: unlink NAPI from device on destruction

Syzbot found a race between tun file and device destruction.
NAPIs live in struct tun_file which can get destroyed before
the netdev so we have to del them explicitly. The current
code is missing deleting the NAPI if the queue was detached
first.

Fixes: 94317099

 ("tun: enable NAPI for TUN/TAP driver")
Reported-by:  <syzbot+b75c138e9286ac742647@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/r/20220623042039.2274708-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>