ixgbe: fix tx queue index

Don't do the num_tx_queues based masking on calculating tx queue
index.

 1) num_tx_queues is not always power-of-2, because it also depends on
    the online cpu numbers. So the masking could be a performance bug
    on a 6 cpu system.
 2) queue_mapping will be limited by real_num_tx_queues=num_tx_queues
    in the generic netdev function set_cur_queue_map(). So the bound
    limiting here is not necessary.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>