ipv6: fix handling of throw routes

It's the same problem that previous fix about blackhole and prohibit routes.

When adding a throw route, it was handled like a classic route.
Moreover, it was only possible to add this kind of routes by specifying
an interface.

Before the patch:
  $ ip route add throw 2001::2/128
  RTNETLINK answers: No such device
  $ ip route add throw 2001::2/128 dev eth0
  $ ip -6 route | grep 2001::2
  2001::2 dev eth0  metric 1024

After:
  $ ip route add throw 2001::2/128
  $ ip -6 route | grep 2001::2
  throw 2001::2 dev lo  metric 1024  error -11

Reported-by: Markus Stenberg <markus.stenberg@iki.fi>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -1471,6 +1471,9 @@ int ip6_route_add(struct fib6_config *cfg)
 		case RTN_PROHIBIT:
 			rt->dst.error = -EACCES;
 			break;
+		case RTN_THROW:
+			rt->dst.error = -EAGAIN;
+			break;
 		default:
 			rt->dst.error = -ENETUNREACH;
 			break;
@@ -2275,7 +2278,8 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	if (rtm->rtm_type == RTN_UNREACHABLE ||
 	    rtm->rtm_type == RTN_BLACKHOLE ||
-	    rtm->rtm_type == RTN_PROHIBIT)
+	    rtm->rtm_type == RTN_PROHIBIT ||
+	    rtm->rtm_type == RTN_THROW)
 		cfg->fc_flags |= RTF_REJECT;
 
 	if (rtm->rtm_type == RTN_LOCAL)
@@ -2412,6 +2416,9 @@ static int rt6_fill_node(struct net *net,
 		case -EACCES:
 			rtm->rtm_type = RTN_PROHIBIT;
 			break;
+		case -EAGAIN:
+			rtm->rtm_type = RTN_THROW;
+			break;
 		default:
 			rtm->rtm_type = RTN_UNREACHABLE;
 			break;