i40e: Fix for VF MAC address 0

After spawning max VFs on a PF, some VFs were not getting resources and
their MAC addresses were 0. This was caused by PF sleeping before flushing
HW registers which caused VIRTCHNL_VFR_VFACTIVE to not be set in time for
VF.

Fix by adding a sleep after hw flush.

Fixes: e4b433f4

 ("i40e: reset all VFs in parallel when rebuilding PF")
Signed-off-by: Sylwester Dziedziuch <sylwesterx.dziedziuch@intel.com>
Signed-off-by: Jan Sokolowski <jan.sokolowski@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>