mac80211: support RX_FLAG_MACTIME_END

Allow drivers to indicate their mactime is at RX completion and adjust
for this in mac80211. Also rename the existing RX_FLAG_MACTIME_MPDU to
RX_FLAG_MACTIME_START to clarify its intent. Based on similar code by
Johannes Berg.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
[fix docs, atheros drivers]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/rtlwifi/rtl8192ce/trx.c

@@ -567,7 +567,7 @@ bool rtl92ce_rx_query_desc(struct ieee80211_hw *hw,
 	if (GET_RX_DESC_RXHT(pdesc))
 		rx_status->flag |= RX_FLAG_HT;
 
-	rx_status->flag |= RX_FLAG_MACTIME_MPDU;
+	rx_status->flag |= RX_FLAG_MACTIME_START;
 
 	if (stats->decrypted)
 		rx_status->flag |= RX_FLAG_DECRYPTED;