virtio-net: xsk: rx: move the xdp->data adjustment to buf_to_xdp()

This commit does not do any functional changes. It moves xdp->data
adjustment for buffer other than first buffer to buf_to_xdp() helper so
that the xdp_buff adjustment does not scatter over different functions.

Signed-off-by: Bui Quang Minh <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/virtio_net.c

···
 		return NULL;
 	}
 
-	xsk_buff_set_size(xdp, len);
+	if (first_buf) {
+		xsk_buff_set_size(xdp, len);
+	} else {
+		xdp_prepare_buff(xdp, xdp->data_hard_start,
+				 XDP_PACKET_HEADROOM - vi->hdr_len, len, 1);
+		xdp->flags = 0;
+	}
+
 	xsk_buff_dma_sync_for_cpu(xdp);
 
 	return xdp;
···
 			goto err;
 		}
 
-		memcpy(buf, xdp->data - vi->hdr_len, len);
+		memcpy(buf, xdp->data, len);
 
 		xsk_buff_free(xdp);