iwlwifi: increase tx_queue debugfs buffer size

For tx_queue, need to increase the buffer size allocated for it,
so all the queues information can be displayed

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>