tipc: set ub->ifindex for local ipv6 address

Without ub->ifindex set for ipv6 address in tipc_udp_enable(),
ipv6_sock_mc_join() may make the wrong dev join the multicast
address in enable_mcast(). This causes that tipc links would
never be created.

So fix it by getting the right netdev and setting ub->ifindex,
as it does for ipv4 address.
Reported-by: Shuang Li <shuali@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/udp_media.c

@@ -738,6 +738,13 @@ static int tipc_udp_enable(struct net *net, struct tipc_bearer *b,
 		b->mtu = b->media->mtu;
 #if IS_ENABLED(CONFIG_IPV6)
 	} else if (local.proto == htons(ETH_P_IPV6)) {
+		struct net_device *dev;
+
+		dev = ipv6_dev_find(net, &local.ipv6);
+		if (!dev) {
+			err = -ENODEV;
+			goto err;
+		}
 		udp_conf.family = AF_INET6;
 		udp_conf.use_udp6_tx_checksums = true;
 		udp_conf.use_udp6_rx_checksums = true;
@@ -745,6 +752,7 @@ static int tipc_udp_enable(struct net *net, struct tipc_bearer *b,
 			udp_conf.local_ip6 = in6addr_any;
 		else
 			udp_conf.local_ip6 = local.ipv6;
+		ub->ifindex = dev->ifindex;
 		b->mtu = 1280;
 #endif
 	} else {