iwlwifi: fix potential lock inversion deadlock

This is a change to a previous patch ("iwlwifi: 3945 split tx_complete
to command and packet function") to ensure we do not have hardirq safe
locks (priv->lock in this case) depend on hardirq unsafe locks.

We only call iwl3945_tx_queue_reclaim while in a tasklet so we have to use
the irqsafe version of the function.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>