wifi: ath11k: fix gtk offload status event locking

In the Linux kernel, the following vulnerability has been resolved: wifi: ath11k: fix gtk offload status event locking The ath11k active pdevs are protected by RCU but the gtk offload status event handling code calling ath11k_mac_get_arvif_by_vdev_id() was not marked as a read-side critical section. Mark the code in question as an RCU read-side critical section to avoid any potential use-after-free issues. Compile tested only.