tuntap: fix dividing by zero in ebpf queue selection

We need check if tun->numqueues is zero (e.g for the persist device)
before trying to use it for modular arithmetic.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: 96f84061("tun: add eBPF based queue selection method")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>