net: hns3: make local functions static

Fixes the following sparse warnings:

drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_ethtool.c:464:5: warning:
 symbol 'hns3_change_all_ring_bd_num' was not declared. Should it be static?
drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_ethtool.c:477:5: warning:
 symbol 'hns3_set_ringparam' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>