* @get_iflink: Get the system interface index associated with the device that
* will be used to send packets (may be different than ifindex for tunnels).
* May be null if the device does not have an iflink.
- * @get_mtu: Get the device's MTU.
+ * @get_mtu: Get the device's MTU. May be %NULL if the device does not have an
+ * MTU (as e.g. some tunnels do not).
* @send: Send a packet on the device. Returns the length of the packet sent.
*/
struct vport_ops {