ipv6: Introduce rt6_nexthop() to select nexthop address.

For RTF_GATEWAY route, return rt->rt6i_gateway.
Otherwise, return 2nd argument (destination address).

This will be used by following patches which remove rt->n
dependency patches in ip6_dst_lookup_tail() and ip6_finish_output2().
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_route.h

@@ -23,6 +23,7 @@ struct route_info {
 #include <net/sock.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
+#include <linux/route.h>
 
 #define RT6_LOOKUP_F_IFACE		0x00000001
 #define RT6_LOOKUP_F_REACHABLE		0x00000002
@@ -194,4 +195,11 @@ static inline int ip6_skb_dst_mtu(struct sk_buff *skb)
 	       skb_dst(skb)->dev->mtu : dst_mtu(skb_dst(skb));
 }
 
+static inline struct in6_addr *rt6_nexthop(struct rt6_info *rt, struct in6_addr *dest)
+{
+	if (rt->rt6i_flags & RTF_GATEWAY)
+		return &rt->rt6i_gateway;
+	return dest;
+}
+
 #endif