net: phy: avoid setting unsupported EEE advertisments

We currently allow userspace to set any EEE advertisments it desires,
whether or not the PHY supports them.  For example:

 # ethtool --set-eee eth1 advertise 0xffffffff
 # ethtool --show-eee eth1
 EEE Settings for eth1:
        EEE status: disabled
        Tx LPI: disabled
        Supported EEE link modes:  100baseT/Full
                                   1000baseT/Full
                                   10000baseT/Full
        Advertised EEE link modes:  100baseT/Full
                                    1000baseT/Full
                                    1000baseKX/Full
                                    10000baseT/Full
                                    10000baseKX4/Full
                                    10000baseKR/Full

Clearly, this is not sane, we should only allow link modes that are
supported to be advertised (as we do elsewhere.)  Ensure that we mask
the MDIO_AN_EEE_ADV value with the capabilities retrieved from the
MDIO_PCS_EEE_ABLE register.

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