net: atlantic: make function 'aq_ethtool_get_priv_flags', 'aq_ethtool_set_priv_flags' static

Fix sparse warnings:

drivers/net/ethernet/aquantia/atlantic/aq_ethtool.c:706:5: warning: symbol 'aq_ethtool_get_priv_flags' was not declared. Should it be static?
drivers/net/ethernet/aquantia/atlantic/aq_ethtool.c:713:5: warning: symbol 'aq_ethtool_set_priv_flags' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: ea4b4d7f ("net: atlantic: loopback tests via private flags")
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>