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: e4b433f ("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>

drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c

@@ -1578,6 +1578,7 @@ bool i40e_reset_vf(struct i40e_vf *vf, bool flr)
 	i40e_cleanup_reset_vf(vf);
 
 	i40e_flush(hw);
+	usleep_range(20000, 40000);
 	clear_bit(I40E_VF_STATE_RESETTING, &vf->vf_states);
 
 	return true;
@@ -1701,6 +1702,7 @@ bool i40e_reset_all_vfs(struct i40e_pf *pf, bool flr)
 	}
 
 	i40e_flush(hw);
+	usleep_range(20000, 40000);
 	clear_bit(__I40E_VF_DISABLE, pf->state);
 
 	return true;