ath9k: Revamp wireless mode usage

Use a single enum for managing modes, store supported modes by
the HW in a bitmask.
Register legacy rates with mac80211 only at init.

Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath9k/xmit.c b/drivers/net/wireless/ath9k/xmit.c
index debd7f4..157f830 100644
--- a/drivers/net/wireless/ath9k/xmit.c
+++ b/drivers/net/wireless/ath9k/xmit.c
@@ -408,7 +408,7 @@
 		if (txctl->min_rate)
 			rcs[0].rix = ath_rate_findrateix(sc, txctl->min_rate);
 		else
-			rcs[0].rix = sc->sc_minrateix;
+			rcs[0].rix = 0;
 		rcs[0].tries = ATH_MGT_TXMAXTRY;
 	}
 	rix = rcs[0].rix;