core: add active connection state DEACTIVATING

Not used yet, but will be when device deactivating state gets
used.  Should be 100% backwards compatible with users that don't
know about it for now.

cli/src/connections.c

@@ -1187,6 +1187,8 @@ active_connection_state_to_string (NMActiveConnectionState state)
 		return _("activating");
 	case NM_ACTIVE_CONNECTION_STATE_ACTIVATED:
 		return _("activated");
+	case NM_ACTIVE_CONNECTION_STATE_DEACTIVATING:
+		return _("deactivating");
 	case NM_ACTIVE_CONNECTION_STATE_UNKNOWN:
 	default:
 		return _("unknown");