net: hns: add skb_reset_mac_header() after skb being alloc

HNS receives a packet without doing anything, but it should call
skb_reset_mac_header() to initialize the header before using
eth_hdr().

Fixes: 0d6b425a
Signed-off-by: Kejian Yan <yankejian@huawei.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>