[][kernel][common][eth][Fix Aquantia link speed mismatch issue for downshift evnent]

[Description]
Fix Aquantia link speed mismatch issue for downshift evnent.

When PHY driver detects a downshift event, it will read the current
link speed from the vendor register. In the meantime, PHY hardware
clears the downshift event and no longer triggers.
In this case, the PHY driver only reports the correct link speed once,
then always reports the incorrect link speed back to PHY framework.

If without this patch, ethtool might read the incorrect link speed
after downshift event occured.

[Release-log]
N/A


Change-Id: I3012b7c8a92c14cbe25b251049cbcbb4a1ef6c09
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7178227
2 files changed