rt2x00: Optimize TX descriptor memory layout

Some fields only need to be u8 and for ifs and txop we can use the
already available enums.

Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00queue.h

@@ -315,17 +315,17 @@ struct txentry_desc {
 
 		struct {
 			u16 mcs;
-			u16 stbc;
-			u16 ba_size;
-			u16 mpdu_density;
-			short txop;
+			u8 stbc;
+			u8 ba_size;
+			u8 mpdu_density;
+			enum txop txop;
 		} ht;
 	} u;
 
 	u16 rate_mode;
 
 	short retry_limit;
-	short ifs;
+	enum ifs ifs;
 
 	enum cipher cipher;
 	u16 key_idx;