team: block mtu change before it happens via NETDEV_PRECHANGEMTU
team: block mtu change before it happens via NETDEV_PRECHANGEMTU

Now it catches the NETDEV_CHANGEMTU notification, which is signaled after
the actual change happened on the device, and returns NOTIFY_BAD, so that
the change on the device is reverted.

This might be quite costly and messy, so use the new NETDEV_PRECHANGEMTU to
catch the MTU change before the actual change happens and signal that it's
forbidden to do it.

CC: Jiri Pirko <1b548d10035ae428195c41f5d55eedb1437ccd8a@resnulli.us>
Signed-off-by: Veaceslav Falico <13e4c2c2c15eff98ad47d02f3ccee2d83dc7015d@redhat.com>
Acked-by: Jiri Pirko <1b548d10035ae428195c41f5d55eedb1437ccd8a@resnulli.us>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs