Staging: vt6655: use is_multicast_ether_addr instead of custom macro

Replace custom macro IS_MULTICAST_ADDRESS by is_multicast_ether_addr
from <linux/etherdevice.h>.
Remove linux/if_ether.h include as it is included in
linux/etherdevice.h already.

Signed-off-by: Charles Clément <caratorn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>