virtio-net: update bytes calculation for xdp_frame

Update relative record value for xdp_frame as basis
for multi-buffer xdp transmission.

Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Heng Qi

drivers/net/virtio_net.c

@@ -665,7 +665,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 		if (likely(is_xdp_frame(ptr))) {
 			struct xdp_frame *frame = ptr_to_xdp(ptr);
 
-			bytes += frame->len;
+			bytes += xdp_get_frame_len(frame);
 			xdp_return_frame(frame);
 		} else {
 			struct sk_buff *skb = ptr;
@@ -1611,7 +1611,7 @@ static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
 		} else {
 			struct xdp_frame *frame = ptr_to_xdp(ptr);
 
-			bytes += frame->len;
+			bytes += xdp_get_frame_len(frame);
 			xdp_return_frame(frame);
 		}
 		packets++;