net/spnic: Fix ethtool loopback command failure

Ramaxel inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4TPKM


CVE: NA

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Fix ethtool loopback command failure

Signed-off-by: Yanling Song <songyl@ramaxel.com>
Reviewed-by: wenliang <wenliang@ramaxel.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>