net: phy: Encapsulate actions performed during link state changes into function phy_adjust_link

During phy state machine state transitions some set of actions should
occur whenever the link state changes. These actions should be
encapsulated into a single function

This patch adds the phy_adjust_link function, which is called whenever
phydev->adjust_link would have been called before. Actions that should
occur whenever the phy link is adjusted can now be added to the
phy_adjust_link function.

Signed-off-by: Zach Brown <zach.brown@ni.com>
Signed-off-by: David S. Miller <davem@davemloft.net>