ixgbe: DCB, remove round robin mode on 82598 devices

Remove round robin configuration code for 82598 parts it
is not settable and is always false.

If we need/want this in the future we can add it back properly.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>