ipv6 mcast: Do not join device multicast for interface-local multicasts.

RFC4291 (IPv6 addressing architecture) says that interface-Local scope
spans only a single interface on a node.  We should not join L2 device
multicast list for addresses in interface-local (or smaller) scope.
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/mcast.c

@@ -661,6 +661,10 @@ static void igmp6_group_added(struct ifmcaddr6 *mc)
 	struct net_device *dev = mc->idev->dev;
 	char buf[MAX_ADDR_LEN];
 
+	if (IPV6_ADDR_MC_SCOPE(&mc->mca_addr) <
+	    IPV6_ADDR_SCOPE_LINKLOCAL)
+		return;
+
 	spin_lock_bh(&mc->mca_lock);
 	if (!(mc->mca_flags&MAF_LOADED)) {
 		mc->mca_flags |= MAF_LOADED;
@@ -687,6 +691,10 @@ static void igmp6_group_dropped(struct ifmcaddr6 *mc)
 	struct net_device *dev = mc->idev->dev;
 	char buf[MAX_ADDR_LEN];
 
+	if (IPV6_ADDR_MC_SCOPE(&mc->mca_addr) <
+	    IPV6_ADDR_SCOPE_LINKLOCAL)
+		return;
+
 	spin_lock_bh(&mc->mca_lock);
 	if (mc->mca_flags&MAF_LOADED) {
 		mc->mca_flags &= ~MAF_LOADED;