firewire net: Send L2 multicast via GASP.

Send L2 multicast packet via GASP (Global asynchronous stream packet) by
seeing the multicast bit in the L2 hardware address, not by seeing upper-
layer protocol address.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>