iwlagn: update write pointers in iwl_irq_tasklet()

Follow-up to "update write pointers for all tx queues after wakeup"; that
patch changed iwl_irq_tasklet_legacy(), but not iwl_irq_tasklet(), so
newer devices were not covered.

Comments from original patch:

Wakeup interrupt has been updating write pointers (indexes, actually) only
for tx queues 0-5.  This is adequate just for 3945, but inadequate for other
devices, all of which have more tx queues.  Now updating all tx/command queues,
so device can be aware of all new tx and host commands enqueued while
device was asleep.

This can potentially improve data traffic bandwidth and/or latency.

Signed-off-by: Ben Cahill <ben.m.cahill@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>