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