ah6: fix error return code in ah6_input()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Link: https://lore.kernel.org/r/1605581105-35295-1-git-send-email-zhangchangzhong@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Zhang Changzhong

net/ipv6/ah6.c

@@ -588,7 +588,8 @@ static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
 	memcpy(auth_data, ah->auth_data, ahp->icv_trunc_len);
 	memset(ah->auth_data, 0, ahp->icv_trunc_len);
 
-	if (ipv6_clear_mutable_options(ip6h, hdr_len, XFRM_POLICY_IN))
+	err = ipv6_clear_mutable_options(ip6h, hdr_len, XFRM_POLICY_IN);
+	if (err)
 		goto out_free;
 
 	ip6h->priority    = 0;