i40e: fix sideband flow director vector allocation

Currently if the MSI-X vector limit is reached the sideband flow
director gets disabled. A bit too early to make that decision, as
vectors may get re-distributed. So move the check further back.

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>