net: hns3: remove redundant assignment of l2_hdr to itself

The pointer l2_hdr is being assigned to itself, this is redundant
and can be removed.

Addresses-Coverity: ("Evaluation order violation")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>