Setting an MTU value below 68 was disabling the network connection and
would not reconnect until the driver was reloaded.  Prevent changing the
MTU to anything below 68.
Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>