net: phy: aquantia: check for changed interface mode in read_status

Depending on the auto-negotiated speed the PHY may change the interface
mode. Check for new mode and set phydev->interface accordingly.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
[hkallweit1@gmail.com: picked from bigger patch and reworked]
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>