net: phy: fix too strict check in phy_start_aneg

When adding checks to detect wrong usage of the phylib API we added
a check to phy_start_aneg() which is too strict. If the phylib
state machine is in state PHY_HALTED we should allow reconfiguring
and restarting aneg, and just don't touch the state.

Fixes: 2b3e88ea ("net: phy: improve phy state checking")
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>