wifi: ath12k: Avoid NULL pointer access during management transmit cleanup

In the Linux kernel, the following vulnerability has been resolved: wifi: ath12k: Avoid NULL pointer access during management transmit cleanup Currently 'ar' reference is not added in skb_cb. Though this is generally not used during transmit completion callbacks, on interface removal the remaining idr cleanup callback uses the ar pointer from skb_cb from management txmgmt_idr. Hence fill them during transmit call for proper usage to avoid NULL pointer dereference. Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1