rocker: Handle protodown notifications.

rocker: Handle protodown notifications.

protodown can be set by user space applications like MLAG on detecting
errors on a switch port. This patch provides sample switch driver changes
for handling protodown. Rocker PHYS disables the port in response to
protodown.

Signed-off-by: Anuradha Karuppiah <[email protected]>
Signed-off-by: Andy Gospodarek <[email protected]>
Signed-off-by: Roopa Prabhu <[email protected]>
Signed-off-by: Wilson Kok <[email protected]>
Signed-off-by: David S. Miller <[email protected]>