i40e: abstract the close path for better netdev vsis

Abstract out the vsi close actions into a single function so they
can be used correctly for both netdev and non-netdev based VSIs.

Change-ID: I59e3d115fcb20e614a09477281b7787dd340d276
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>