virtio-net: make rx buf size estimation works for XDP

We don't update ewma rx buf size in the case of XDP. This will lead
underestimation of rx buf size which causes host to produce more than
one buffers. This will greatly increase the possibility of XDP page
linearization.

Cc: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -584,10 +584,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 				put_page(page);
 				head_skb = page_to_skb(vi, rq, xdp_page,
 						       0, len, PAGE_SIZE);
+				ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 				return head_skb;
 			}
 			break;
 		case XDP_TX:
+			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			if (unlikely(xdp_page != page))
 				goto err_xdp;
 			rcu_read_unlock();
@@ -596,6 +598,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		default:
 			if (unlikely(xdp_page != page))
 				__free_pages(xdp_page, 0);
+			ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
 			goto err_xdp;
 		}
 	}