[][kernel][common][eth][Add a link down recovery handler for the SGMII]

[Description]
Add a link down recovery handler for the SGMII.

In order to prevent any abnormal network behavior caused by this link
failure, we have added an error handler to recover the connection of
the SGMII.

Without this patch, the driver cannot prevent any abnormal network
behavior caused by link failure of the SGMII.

[Release-log]
N/A


Change-Id: Iba017416a5e5cc8298662c06b27bc35206365ef0
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8447559
2 files changed