There's only a few places left where the net_device back-pointer from
struct net_local is used, so we can reduce the private struct size by
removing it.
Remove it entirely by using the net_device already passed to the
function in question and by storing the net_device pointer instead of
the net_local pointer in mii_bus->priv.
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>