ibmvnic: Return failure on attempted mtu change

Changing the mtu is currently not supported in the ibmvnic driver.

Implement .ndo_change_mtu in the driver so that attempting to use ifconfig
to change the mtu will fail and present the user with an error message.

Signed-off-by: John Allen <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/ibm/ibmvnic.c

···
 }
 #endif
 
+static int ibmvnic_change_mtu(struct net_device *netdev, int new_mtu)
+{
+	return -EOPNOTSUPP;
+}
+
 static const struct net_device_ops ibmvnic_netdev_ops = {
 	.ndo_open		= ibmvnic_open,
 	.ndo_stop		= ibmvnic_close,
···
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	.ndo_poll_controller	= ibmvnic_netpoll_controller,
 #endif
+	.ndo_change_mtu		= ibmvnic_change_mtu,
 };
 
 /* ethtool functions */