iwlwifi: need check for valid qos packet before free

For 4965, need to check it is valid qos frame before free, only valid
QoS frame has the tid used to free the packets.

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