macvlan: broadcast addr should be part of mc_filter

commit cd431e73 (macvlan: add multicast filter) forgot
the broadcast case.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Maciej Żenczykowski <maze@google.com>
SIgned-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>