iwlwifi: update tx command response status

Update to include additional tx command response status for "_agn"
devices.

The following status indicate the transmission was postponed:
  TX_STATUS_POSTPONE_DELAY
  TX_STATUS_POSTPONE_FEW_BYTES
  TX_STATUS_POSTPONE_BT_PRIO
  TX_STATUS_POSTPONE_QUIET_PERIOD
  TX_STATUS_POSTPONE_CALC_TTAK

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>