ipc: Change ipc socket's owner to $default_internal_user

This is mainly used by director process, which runs as
$default_internal_user. This setting change is always required for director
installations. Also the ipc process itself is already running as
$default_internal_user so this should be a rather safe change.

src/ipc/ipc-settings.c

@@ -9,7 +9,7 @@
 
 /* <settings checks> */
 static struct file_listener_settings ipc_unix_listeners_array[] = {
-	{ "ipc", 0600, "", "" },
+	{ "ipc", 0600, "$default_internal_user", "" },
 	{ "login/ipc-proxy", 0600, "$default_login_user", "" }
 };
 static struct file_listener_settings *ipc_unix_listeners[] = {