b44: use netdev_alloc_skb_ip_align()

Without this patch b44 always allocates the 2 bytes needed for aligned
access on every platform, now it uses netdev_alloc_skb_ip_align().

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: David S. Miller <davem@davemloft.net>