ip6_tunnel: allow routing IPv4 traffic in NBMA mode

Since IPv4 routes support IPv6 gateways now, we can route IPv4 traffic in
NBMA tunnels.
Signed-off-by: Qing Deng <i@moy.cat>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_tunnel.c

@@ -1121,6 +1121,11 @@ int ip6_tnl_xmit(struct sk_buff *skb, struct net_device *dev, __u8 dsfield,
 
 			memcpy(&fl6->daddr, addr6, sizeof(fl6->daddr));
 			neigh_release(neigh);
+		} else if (skb->protocol == htons(ETH_P_IP)) {
+			struct rtable *rt = skb_rtable(skb);
+
+			if (rt->rt_gw_family == AF_INET6)
+				memcpy(&fl6->daddr, &rt->rt_gw6, sizeof(fl6->daddr));
 		}
 	} else if (t->parms.proto != 0 && !(t->parms.flags &
 					    (IP6_TNL_F_USE_ORIG_TCLASS |