net: bcmgenet: manipulate netdev_queue directly

Instead of always invoking netdev_get_tx_queue() in bcmgenet_xmit() and
bcmgenet_tx_reclaim(), just get the corresponding netdev_queue pointer
once and for all and manipulate it throughout bcmgenet_xmit() and
bcmgenet_tx_reclaim().

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>