qcacmn: Add enum for invalid htt stat type

Add enumeration for invalid stat type htt_cmn_dbg_stats_type for
ol_txrx_stats_callback handler.

Change-Id: I8a976737af8f226a1774950170f445c93ebf683b
CRs-Fixed: 2215678

dp/inc/cdp_txrx_cmn_struct.h

@@ -171,7 +171,8 @@ enum htt_cmn_dbg_stats_type {
 	/* bits 18-23 currently reserved */
 
 	/* keep this last */
-	HTT_DBG_CMN_NUM_STATS
+	HTT_DBG_CMN_NUM_STATS,
+	HTT_DBG_CMN_NUM_STATS_INVALID        = 31, /* bit 31 -> 0x80000000 */
 };
 
 /*