rt2x00: Fix EIFS timing value

Olivier reported a difference between the EIFS
values used in the legacy driver and the one in
the rt2x00 drivers.

In rt2x00 the value was
	( SIFS + (8 * (IEEE80211_HEADER + ACK_SIZE)) )
which comes down to 314us while the legacy driver uses the value 364us

This was caused because EIFS is: SIFS + DIFS + AckTime
This patch will fix this by adding the DIFS by the above value,
and creating a SHORT_EIFS define which uses the SHORT_DIFS.
Reported-by: Olivier Cornu <o.cornu@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00.h

@@ -108,7 +108,10 @@
 #define SHORT_PIFS		( SIFS + SHORT_SLOT_TIME )
 #define DIFS			( PIFS + SLOT_TIME )
 #define SHORT_DIFS		( SHORT_PIFS + SHORT_SLOT_TIME )
-#define EIFS			( SIFS + (8 * (IEEE80211_HEADER + ACK_SIZE)) )
+#define EIFS			( SIFS + DIFS + \
+				  (8 * (IEEE80211_HEADER + ACK_SIZE)) )
+#define SHORT_EIFS		( SIFS + SHORT_DIFS + \
+				  (8 * (IEEE80211_HEADER + ACK_SIZE)) )
 
 /*
  * Chipset identification

drivers/net/wireless/rt2x00/rt2x00config.c

@@ -271,7 +271,7 @@ config:
 		libconf.sifs = SIFS;
 		libconf.pifs = short_slot_time ? SHORT_PIFS : PIFS;
 		libconf.difs = short_slot_time ? SHORT_DIFS : DIFS;
-		libconf.eifs = EIFS;
+		libconf.eifs = short_slot_time ? SHORT_EIFS : EIFS;
 	}
 
 	libconf.conf = conf;