It doesn't make sense to rewrite all these registers every time the PHY
library notifies us about a link state change.

In a future patch we will customize the MTU for the CPU port, and since
the MTU was previously configured from adjust_link, if we don't make
this change, its value would have got overridden.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>