i40e: refactor repeated link state reporting code

Refactor repeated link state reporting code into a separate helper
functions: i40e_set_vf_link_state() i40e_vc_link_speed2mbps().
Add support of VIRTCHNL_VF_CAP_ADV_LINK_SPEED;

Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>