qcacmn: Add fix to set NULL to msdu extn desc on release

Add fix to set NULL to msdu extn descriptor on release.
if same descriptor is used for other frame type. there is a more chance
extension descriptor can be added to the same free list.

Change-Id: I25e86c0ae03b4b39b6813519864afd16b3d19e4c
CRs-Fixed: 3503237

dp/wifi3.0/dp_tx.c

@@ -404,6 +404,8 @@ dp_tx_desc_release(struct dp_soc *soc, struct dp_tx_desc_s *tx_desc,
 					  tx_desc->msdu_ext_desc->me_buffer);
 
 		dp_tx_ext_desc_free(soc, tx_desc->msdu_ext_desc, desc_pool_id);
+
+		tx_desc->msdu_ext_desc = NULL;
 	}
 
 	if (tx_desc->flags & DP_TX_DESC_FLAG_TO_FW)