sfc_ef100: plumb in fini_dmaq

Bring down the TX and RX queues at ifdown, so that we can then fini the
 EVQs (otherwise the MC would return EBUSY because they're still in use).

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>