iwl3945: sync tx queue data structure with iwlagn

We are now using the iwl_tx_queue for iwl3945. To reach that goal, we
included the 3945 specific tfd frame structure to iwl_tx_queue. This
has no effect on the current iwlagn code.

Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>