[NET]: Don't exclude broadcast addresses from is_multicast_ether_addr()

The check for multicast shouldn't exclude broadcast type addresses.
This reverts the incorrect change done in 2.6.13.

The broadcast address is a multicast address and should be excluded
from being a valid_ether_address for use in bridging or device address.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>