mlx4: Fix tx ring affinity_mask creation

By default, the number of tx queues is limited by the number of online cpus
in mlx4_en_get_profile(). However, this limit no longer holds after the
ethtool .set_channels method has been called. In that situation, the driver
may access invalid bits of certain cpumask variables when queue_index >=
nr_cpu_ids.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Acked-by: Ido Shamay <idos@mellanox.com>
Fixes: d03a68f8 ("net/mlx4_en: Configure the XPS queue mapping on driver load")
Signed-off-by: David S. Miller <davem@davemloft.net>