[IPV6]: Introduce ip6_dst_idev() to get inet6_dev{} stored in dst_entry{}.

Otherwise, we will see a lot of casts...
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

include/net/ip6_fib.h

@@ -107,6 +107,11 @@ struct rt6_info
 	u8				rt6i_protocol;
 };
 
+static inline struct inet6_dev *ip6_dst_idev(struct dst_entry *dst)
+{
+	return ((struct rt6_info *)dst)->rt6i_idev;
+}
+
 struct fib6_walker_t
 {
 	struct fib6_walker_t *prev, *next;

net/ipv6/addrconf.c

@@ -1164,7 +1164,7 @@ record_it:
 int ipv6_get_saddr(struct dst_entry *dst,
 		   struct in6_addr *daddr, struct in6_addr *saddr)
 {
-	return ipv6_dev_get_saddr(dst ? ((struct rt6_info *)dst)->rt6i_idev->dev : NULL, daddr, saddr);
+	return ipv6_dev_get_saddr(dst ? ip6_dst_idev(dst)->dev : NULL, daddr, saddr);
 }
 
 

net/ipv6/ip6_input.c

@@ -84,7 +84,7 @@ int ipv6_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt
 	 * arrived via the sending interface (ethX), because of the
 	 * nature of scoping architecture. --yoshfuji
 	 */
-	IP6CB(skb)->iif = skb->dst ? ((struct rt6_info *)skb->dst)->rt6i_idev->dev->ifindex : dev->ifindex;
+	IP6CB(skb)->iif = skb->dst ? ip6_dst_idev(skb->dst)->dev->ifindex : dev->ifindex;
 
 	if (unlikely(!pskb_may_pull(skb, sizeof(*hdr))))
 		goto err;