xen-netback: fix fragments error handling in checksum_setup_ip()

Fix to return -EPROTO error if fragments detected in checksum_setup_ip().

Fixes: 1431fb31 ('xen-netback: fix fragment detection in checksum setup')
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: NPaul Durrant <paul.durrant@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -1197,6 +1197,9 @@ static int checksum_setup_ip(struct xenvif *vif, struct sk_buff *skb,
 
 	err = -EPROTO;
 
+	if (fragment)
+		goto out;
+
 	switch (ip_hdr(skb)->protocol) {
 	case IPPROTO_TCP:
 		err = maybe_pull_tail(skb,