netfilter: xt_HL: prefer skb_ensure_writable

Also, make the argument to be only the needed size of the header
we're altering, no need to pull in the full packet into linear area.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/xt_HL.c

@@ -32,7 +32,7 @@ ttl_tg(struct sk_buff *skb, const struct xt_action_param *par)
 	const struct ipt_TTL_info *info = par->targinfo;
 	int new_ttl;
 
-	if (!skb_make_writable(skb, skb->len))
+	if (skb_ensure_writable(skb, sizeof(*iph)))
 		return NF_DROP;
 
 	iph = ip_hdr(skb);
@@ -72,7 +72,7 @@ hl_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 	const struct ip6t_HL_info *info = par->targinfo;
 	int new_hl;
 
-	if (!skb_make_writable(skb, skb->len))
+	if (skb_ensure_writable(skb, sizeof(*ip6h)))
 		return NF_DROP;
 
 	ip6h = ipv6_hdr(skb);