xen-netback: use skb_is_gso in xenvif_start_xmit

In 5bd076708 ("Xen-netback: Fix issue caused by using gso_type wrongly")
we use skb_is_gso to determine if we need an extra slot to accommodate
the SKB. There's similar error in interface.c. Change that to use
skb_is_gso as well.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Annie Li <annie.li@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/interface.c

@@ -132,8 +132,7 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* If the skb is GSO then we'll also need an extra slot for the
 	 * metadata.
 	 */
-	if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
-	    skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
+	if (skb_is_gso(skb))
 		min_slots_needed++;
 
 	/* If the skb can't possibly fit in the remaining slots