mac80211: replace some dead code by a warning

Given the (nested) switch statements, this code can't
be reached, so make it warn instead of manipulating
the carrier state which seems purposeful.
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

@@ -581,7 +581,8 @@ int ieee80211_do_open(struct wireless_dev *wdev, bool coming_up)
 		case NL80211_IFTYPE_P2P_DEVICE:
 			break;
 		default:
-			netif_carrier_on(dev);
+			/* not reached */
+			WARN_ON(1);
 		}
 
 		/*