ifcfg-rh: correct the error handling for NM_CONTROLLED=no connections

We ought to set an error if we're returning NULL from
connection_from_file_full(). Also, printing out a warning ourselves makes no
sense -- the caller communicates this if we signal an error by returning NULL.

src/settings/plugins/ifcfg-rh/reader.c

@@ -4736,7 +4736,8 @@ connection_from_file_full (const char *filename,
 
 		connection = create_unhandled_connection (filename, parsed, "unmanaged", out_unhandled);
 		if (!connection)
-			PARSE_WARNING ("NM_CONTROLLED was false but device was not uniquely identified; device will be managed");
+			g_set_error (error, NM_SETTINGS_ERROR, NM_SETTINGS_ERROR_FAILED,
+			             "NM_CONTROLLED was false but device was not uniquely identified; device will be managed");
 		goto done;
 	}