esp6: fix incorrect null pointer check on xo

The check for xo being null is incorrect, currently it is checking
for non-null, it should be checking for null.

Detected with CoverityScan, CID#1429349 ("Dereference after null check")

Fixes: 7862b4058b9f ("esp: Add gso handlers for esp4 and esp6")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c
index 1cceeee..95f10728 100644
--- a/net/ipv6/esp6_offload.c
+++ b/net/ipv6/esp6_offload.c
@@ -120,7 +120,7 @@
 	netdev_features_t esp_features = features;
 	struct xfrm_offload *xo = xfrm_offload(skb);
 
-	if (xo)
+	if (!xo)
 		goto out;
 
 	seq = xo->seq.low;