The guest virtio device may request MTU updating when the vhost backend
device exposes a capability to support it.
Expose the MTU feature capability.
At configuration time, check the requested MTU and update it in the HW
device.
Signed-off-by: Matan Azrad <matan@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>