The station control register must depend on both the advertisement and the lpa

The link partner ability has better be intersected with the current
advertised value before it is feed to the station control register.
Sight-catched-by: Lars Vahlenberg <lars.vahlenberg@gmail.com>
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>