i40e: Save off VSI resource count when updating VSI

When updating a VSI, save off the number of allocated and unallocated
VSIs as we do when adding a VSI.

Signed-off-by: Kevin Scott <kevin.c.scott@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>