Documentation: net: phy: reflect latest changes to phylib API

Recent changes to the phylib API
- removed phy_stop_interrupts
- replaced phy_start_interrupts with phy_request_interrupt
- moved some functionality from phy_connect() and phy_disconnect()
  to phy_start() and phy_stop() respectively.
Reflect these changes in the documentation.

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