Add comments to some driver data structures

Remove unused "sched_retry" member from struct iwl3945_tx_queue
Signed-off-by: NBen Cahill <ben.m.cahill@intel.com>
Signed-off-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>