esp6: fix memleak on error path in esp6_input

This ought to be an omission in e619492323 ("esp: Fix memleaks on error
paths."). The memleak on error path in esp6_input is similar to esp_input
of esp4.

Fixes: e619492323 ("esp: Fix memleaks on error paths.")
Fixes: 3f29770723 ("ipsec: check return value of skb_to_sgvec always")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv6/esp6.c

@@ -669,8 +669,10 @@ skip_cow:
 
 	sg_init_table(sg, nfrags);
 	ret = skb_to_sgvec(skb, sg, 0, skb->len);
-	if (unlikely(ret < 0))
+	if (unlikely(ret < 0)) {
+		kfree(tmp);
 		goto out;
+	}
 
 	skb->ip_summed = CHECKSUM_NONE;