[NETFILTER]: annotate xtables targets with const and remove casts

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/ipv6/netfilter/ip6t_REJECT.c

@@ -41,7 +41,8 @@ static void send_reset(struct sk_buff *oldskb)
 	struct tcphdr otcph, *tcph;
 	unsigned int otcplen, hh_len;
 	int tcphoff, needs_ack;
-	struct ipv6hdr *oip6h = ipv6_hdr(oldskb), *ip6h;
+	const struct ipv6hdr *oip6h = ipv6_hdr(oldskb);
+	struct ipv6hdr *ip6h;
 	struct dst_entry *dst = NULL;
 	u8 proto;
 	struct flowi fl;

net/ipv6/netfilter/ip6t_ipv6header.c

@@ -49,7 +49,8 @@ ipv6header_mt6(const struct sk_buff *skb, const struct net_device *in,
 	temp = 0;
 
 	while (ip6t_ext_hdr(nexthdr)) {
-		struct ipv6_opt_hdr _hdr, *hp;
+		const struct ipv6_opt_hdr *hp;
+		struct ipv6_opt_hdr _hdr;
 		int hdrlen;
 
 		/* Is there enough space for the next ext header? */

net/ipv6/netfilter/ip6t_rt.c

@@ -110,7 +110,8 @@ rt_mt6(const struct sk_buff *skb, const struct net_device *in,
 		!!(rtinfo->invflags & IP6T_RT_INV_TYP)));
 
 	if (ret && (rtinfo->flags & IP6T_RT_RES)) {
-		u_int32_t *rp, _reserved;
+		const u_int32_t *rp;
+		u_int32_t _reserved;
 		rp = skb_header_pointer(skb,
 					ptr + offsetof(struct rt0_hdr,
 						       reserved),