vfio-pci: Release all MSI-X vectors when disabled

We were relying on msix_unset_vector_notifiers() to release all the
vectors when we disable MSI-X, but this only happens when MSI-X is
still enabled on the device.  Perform further cleanup by releasing
any remaining vectors listed as in-use after this call.  This caused
a leak of IRQ routes on hotplug depending on how the guest OS prepared
the device for removal.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: qemu-stable@nongnu.org
