net: tun: unlink NAPI from device on destruction

In the Linux kernel, the following vulnerability has been resolved: 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.