net: bcmgenet: set hw_params->rx_queues = 0

bcmgenet driver doesn't yet support multiple Rx queues.
Set hw_params->rx_queues = 0 accordingly.
The default Rx queue (Q16) is still created and operational.

Signed-off-by: Petri Gynther <pgynther@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>