A typical 100Base-T1 link should be always connected. If the link is in
a shot or open state, it is a failure. In most cases, we won't be able
to automatically handle this issue, but we need to log it or notify user
(if possible).

With this patch, the cable will be tested on "ip l s dev .. up" attempt
and send ethnl notification to the user space.

This patch was tested with TJA1102 PHY and "ethtool --monitor" command.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>