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

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

Fixes: 1431fb31ecba ('xen-netback: fix fragment detection in checksum setup')
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index e884ee1..27bbe58 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1197,6 +1197,9 @@
 
 	err = -EPROTO;
 
+	if (fragment)
+		goto out;
+
 	switch (ip_hdr(skb)->protocol) {
 	case IPPROTO_TCP:
 		err = maybe_pull_tail(skb,