qtnfmac: use __netdev_alloc_skb_ip_align

Replace __dev_alloc_skb and explicit NET_IP_ALIGN alignment by built-in
__netdev_alloc_skb_ip_align function.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>