virtio_net: add the total stats field

Now, we just show the stats of every queue.

But for the user, the total values of every stat may are valuable.

NIC statistics:
     rx_packets: 373522
     rx_bytes: 85919736
     rx_drops: 0
     rx_xdp_packets: 0
     rx_xdp_tx: 0
     rx_xdp_redirects: 0
     rx_xdp_drops: 0
     rx_kicks: 11125
     rx_hw_notifications: 0
     rx_hw_packets: 1325870
     rx_hw_bytes: 263348963
     rx_hw_interrupts: 0
     rx_hw_drops: 1451
     rx_hw_drop_overruns: 0
     rx_hw_csum_valid: 1325870
     rx_hw_needs_csum: 1325870
     rx_hw_csum_none: 0
     rx_hw_csum_bad: 0
     rx_hw_ratelimit_packets: 0
     rx_hw_ratelimit_bytes: 0
     tx_packets: 10050
     tx_bytes: 1230176
     tx_xdp_tx: 0
     tx_xdp_tx_drops: 0
     tx_kicks: 10050
     tx_timeouts: 0
     tx_hw_notifications: 0
     tx_hw_packets: 32281
     tx_hw_bytes: 4315590
     tx_hw_interrupts: 0
     tx_hw_drops: 0
     tx_hw_drop_malformed: 0
     tx_hw_csum_none: 0
     tx_hw_needs_csum: 32281
     tx_hw_ratelimit_packets: 0
     tx_hw_ratelimit_bytes: 0
     rx0_packets: 373522
     rx0_bytes: 85919736
     rx0_drops: 0
     rx0_xdp_packets: 0
     rx0_xdp_tx: 0
     rx0_xdp_redirects: 0
     rx0_xdp_drops: 0
     rx0_kicks: 11125
     rx0_hw_notifications: 0
     rx0_hw_packets: 1325870
     rx0_hw_bytes: 263348963
     rx0_hw_interrupts: 0
     rx0_hw_drops: 1451
     rx0_hw_drop_overruns: 0
     rx0_hw_csum_valid: 1325870
     rx0_hw_needs_csum: 1325870
     rx0_hw_csum_none: 0
     rx0_hw_csum_bad: 0
     rx0_hw_ratelimit_packets: 0
     rx0_hw_ratelimit_bytes: 0
     tx0_packets: 10050
     tx0_bytes: 1230176
     tx0_xdp_tx: 0
     tx0_xdp_tx_drops: 0
     tx0_kicks: 10050
     tx0_timeouts: 0
     tx0_hw_notifications: 0
     tx0_hw_packets: 32281
     tx0_hw_bytes: 4315590
     tx0_hw_interrupts: 0
     tx0_hw_drops: 0
     tx0_hw_drop_malformed: 0
     tx0_hw_csum_none: 0
     tx0_hw_needs_csum: 32281
     tx0_hw_ratelimit_packets: 0
     tx0_hw_ratelimit_bytes: 0

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>