i40e: warn on double free

Down was requesting queue disables, but then exited immediately without
waiting for the queues to actually disable. This could allow any
function called after i40evf_down to run immediately, including
i40evf_up, and causes a memory leak.

This issue has been fixed in a recent refactor of the reset code, but
add a couple WARN_ONs in the slow path to help us recognize if we
reintroduce this issue or if we missed any cases.

Change-ID: I27b6b5c9a79c1892f0ba453129f116bc32647dd0
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>