i40e/base: add parsing for CEE DCBX TLVs

i40e/base: add parsing for CEE DCBX TLVs

This patch adds parsing for CEE DCBX TLVs from the LLDP MIB.

While the driver gets the DCB CEE operational configuration from Firmware
using the "Get CEE DCBX Oper Config" AQ command there is a need to get
the CEE DesiredCfg Tx by firmware and DCB configuration Rx from peer; for
debug and other application purposes.

Also gets rid of unused locals variables.

Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>
Tested-by: Huilong Xu <huilongx.xu@intel.com>