ixgbe: move setting of GSO size for 82598 into ixgbe_configure_dcb

We are unnecessarily modifying the GSO size for all HW when we don't need
to.  The code can be simplified by moving the check for DCB and the
adjustment of the GSO size for 82598 into ixgbe_configure_dcb.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>