ice: Copy dcbx configuration only if mode is correct

In rebuild DCB desired_dcbx_cfg was copy to local_dcbx_cfg, but
if DCBX mode is IEEE desired_dcbx_cfg is not initialized by DCBX
config from FW. Change logic to copy config value only if mode is
set to CEE.

If driver copy desired_dcbx_cfg to local_dcbx_cfg in IEEE mode there
is problem with globr. System is frozen after two or more globr.

Signed-off-by: Michal Swiatkowski <michal.swiatkowski@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>