When the user sets a non-zero coalescing parameter to 0 for a specific
virtqueue, it does not work as expected, so let's fix this.

Fixes: 394bd877 ("virtio_net: support per queue interrupt coalesce command")
Reported-by: Xiaoming Zhao <zxm377917@alibaba-inc.com>
Cc: Gavin Li <gavinl@nvidia.com>
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>