net: phy: start state machine in phy_start only

The state machine is a no-op before phy_start() has been called.
Therefore let's enable it in phy_start() only. In phy_start()
let's call phy_start_machine() instead of phy_trigger_machine().
phy_start_machine is an alias for phy_trigger_machine but it makes
clearer that we start the state machine here instead of just
triggering a run.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>