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/offchannel.c b/net/mac80211/offchannel.c
index faf4f60..f1d40b6 100644
--- a/net/mac80211/offchannel.c
+++ b/net/mac80211/offchannel.c
@@ -801,14 +801,14 @@ int ieee80211_mgmt_tx(struct wiphy *wiphy, struct wireless_dev *wdev,
 	case NL80211_IFTYPE_ADHOC:
 		if (!sdata->vif.bss_conf.ibss_joined)
 			need_offchan = true;
-		/* fall through */
 #ifdef CONFIG_MAC80211_MESH
+		/* fall through */
 	case NL80211_IFTYPE_MESH_POINT:
 		if (ieee80211_vif_is_mesh(&sdata->vif) &&
 		    !sdata->u.mesh.mesh_id_len)
 			need_offchan = true;
-		/* fall through */
 #endif
+		/* fall through */
 	case NL80211_IFTYPE_AP:
 	case NL80211_IFTYPE_AP_VLAN:
 	case NL80211_IFTYPE_P2P_GO: