mac80211: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Notice that in some cases I replaced "fall through on else" and
"otherwise fall through" comments with just a "fall through" comment,
which is what GCC is expecting to find.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index c244691..fa0f96c 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -473,6 +473,7 @@ static void ieee80211_add_ht_ie(struct ieee80211_sub_if_data *sdata,
 	case IEEE80211_SMPS_AUTOMATIC:
 	case IEEE80211_SMPS_NUM_MODES:
 		WARN_ON(1);
+		/* fall through */
 	case IEEE80211_SMPS_OFF:
 		cap |= WLAN_HT_CAP_SM_PS_DISABLED <<
 			IEEE80211_HT_CAP_SM_PS_SHIFT;