mace: Fix build for mace due to netdev_alloc_skb

Refs:
1. pmac32_defconfig
http://kisskb.ellerman.id.au/kisskb/buildresult/5583746/
2. ppc6xx_defconfig
http://kisskb.ellerman.id.au/kisskb/buildresult/5584116/

Confirmed any such occurances from all failed defconfigs &
in net-next sources with
grep -nrs "netdev_alloc_skb" drivers/net/ethernet/ | grep -v ","

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Pradeep A Dalvi <netdev@pradeepdalvi.com>
Signed-off-by: David S. Miller <davem@davemloft.net>