Once the RTNL locking around the control buffer is removed there can be
contention on the per queue RX interrupt coalescing data. Use a mutex
per queue. A mutex is required because virtnet_send_command can sleep.
Signed-off-by: Daniel Jurgens <danielj@nvidia.com> Reviewed-by: Heng Qi <hengqi@linux.alibaba.com> Tested-by: Heng Qi <hengqi@linux.alibaba.com> Acked-by: Jason Wang <jasowang@redhat.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com>