qcacld-3.0: Fix race vdev down and tx_desc->vdev access

ol_tx_update_arp_stats() in tx completion path updates the per vdev
arp statistics. vdev is referenced from tx_desc.
In cases when vdev has gone down and tx completion are received leads
to NULL vdev access. So clear reference to vdev inside tx_descs when
vdev goes down.

Change-Id: Ic8c854b42ece41489f71e1374e5e72580308e9fe
CRs-Fixed: 2215312
2 files changed