qcacld-3.0: Avoid access of deleted peer during RX thread close

During SSR case in wlan_hdd_stop_modules(), ol_txrx_pdev_pre_detach()
cleanup the peer forcibly. Later RX Thread is getting closed as part
of cds_sched_close(). So chances of accessing deleted peer is there.

Shutdown RX thread before doing ol_txrx_pdev_pre_detach() to avoid
the chances of accessing deleted peer.

Change-Id: Iae27262396d8245eeb7a9b39cb678fad14815260
CRs-Fixed: 2349994