net: ethernet: dnet: don't call dev_kfree_skb() under spin_lock_irqsave()

It is not allowed to call kfree_skb() or consume_skb() from hardware
interrupt context or with hardware interrupts being disabled.

In this case, the lock is used to protected 'bp', so we can move
dev_kfree_skb() after the spin_unlock_irqrestore().

Fixes: 47964174 ("dnet: Dave DNET ethernet controller driver (updated)")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>