qemu: skip hardcoded hostdev migration check if QEMU can do it for us

qemu: skip hardcoded hostdev migration check if QEMU can do it for us

libvirt currently will block migration for any vfio-assigned device
unless it is a network device that is associated with a virtio-net
failover device (ie. if the hostdev object has a teaming->type ==
VIR_DOMAIN_NET_TEAMING_TYPE_TRANSIENT).

In the future there will be other vfio devices that can be migrated,
so we don't want to rely on this hardcoded block. QEMU 6.0+ will
anyway inform us of any devices that will block migration (as a part
of qemuDomainGetMigrationBlockers()), so we only need to do the
hardcoded check in the case of old QEMU that can't provide that
information.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Jiri Denemark <jdenemar@redhat.com>