rtl8180: report mac80211 short preamble RX flag

This patch make it possible to mac80211 to know whether a frame
has been received with short preamble.

It simply checks for the "splcp" flag in the RX status
descriptor, and eventually set RX_FLAG_SHORTPRE in mac80211
rx status structure.

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtl818x/rtl8180/dev.c

@@ -284,6 +284,8 @@ static void rtl8180_handle_rx(struct ieee80211_hw *dev)
 			rx_status.band = dev->conf.chandef.chan->band;
 			rx_status.mactime = tsft;
 			rx_status.flag |= RX_FLAG_MACTIME_START;
+			if (flags & RTL818X_RX_DESC_FLAG_SPLCP)
+				rx_status.flag |= RX_FLAG_SHORTPRE;
 			if (flags & RTL818X_RX_DESC_FLAG_CRC32_ERR)
 				rx_status.flag |= RX_FLAG_FAILED_FCS_CRC;