net: hns3: add ethtool priv-flag for TX push

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4QHSV



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Add a control private flag in ethtool for enable/disable
TX push feature.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>