net: phy: add genphy_check_and_restart_aneg()

Add a helper for restarting autonegotiation(), similar to the clause 45
variant.  Use it in __genphy_config_aneg()

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>