- * If successful, returns 0 and stores the MTU size in '*mtup'. On failure,
- * returns a positive errno value and stores ETH_PAYLOAD_MAX (1500) in
+ * If successful, returns 0 and stores the MTU size in '*mtup'. Stores INT_MAX
+ * in '*mtup' if 'netdev' does not have an MTU (as e.g. some tunnels do not).On
+ * failure, returns a positive errno value and stores ETH_PAYLOAD_MAX (1500) in