qcacmn: update tx flags for radiotap header prepare

Currently radiotap header is malformed due to incorrect
tx flags update.

This change is update tx flags properly to prepare radiotap
header.

Change-Id: I0d3205b215c9fc363a71c4e7a6b54e40fb10a966
CRs-Fixed: 3442934

qdf/linux/src/qdf_nbuf.c

@@ -5331,7 +5331,7 @@ unsigned int qdf_nbuf_update_radiotap(struct mon_rx_status *rx_status,
 
 	/* update tx flags for pkt capture*/
 	if (rx_status->add_rtap_ext) {
-		rthdr->it_present |=
+		it_present_val |=
 			cpu_to_le32(1 << IEEE80211_RADIOTAP_TX_FLAGS);
 		rtap_len = qdf_nbuf_update_radiotap_tx_flags(rx_status,
 							     rtap_buf,