The current dts file of dgs-1210-10p doesn't support link states
for the sfp ports (they are always up).
This patch tries to give better support for this and was run tested
on dgs-1210-10p.
It was heavily inspired from Paul Fertser, RaylynnKnight
and the author of dgs-1210-10mp-f.dts
https://forum.openwrt.org/t/dlink-dgs-1210-10p-with-glc-t-co-sfp/170928
Signed-off-by: Michel Thill <jmthill@gmail.com>
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