net: phy: fix interrupt handling in non-started states

phylib enables interrupts before phy_start() has been called, and if
we receive an interrupt in a non-started state, the interrupt handler
returns IRQ_NONE. This causes problems with at least one Marvell chip
as reported by Andrew.
Fix this by handling interrupts the same as in phy_mac_interrupt(),
basically always running the phylib state machine. It knows when it
has to do something and when not.
This change allows to handle interrupts gracefully even if they
occur in a non-started state.

Fixes: 2b3e88ea ("net: phy: improve phy state checking")
Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.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>