amd-xgbe: Use napi_alloc_skb when allocating skb in softirq

Use the napi_alloc_skb function to allocate an skb when running within
the softirq context to avoid calls to local_irq_save/restore.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>