unlike documented may not take effect without an initialization. So
don't invoke (*sc_mediachange) directly in lance_mediachange() but
go through lance_init_locked(). It's suboptimal to impose this for
all chips but given that besides the affected PCI bus front-end the
only other front-end which supports media selection is and likely
ever will be the 'ledma' front-end I see not enough reason to break
the in-driver API for this (though one could argue both ways here).