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>