qemu_hotplug: don't forget to add hostdev interfaces to the interface list

qemu_hotplug: don't forget to add hostdev interfaces to the interface list

Originally qemuDomainAttachNetDevice() would wait until the cleanup at
the very end of the function to add newly hotplugged interfaces to the
domain's nets list. commit 7b8bec4560 modified it to add the new
interface to the nets list earlier (but not all the way at the
beginning of the function either, because there are some operations
(PCI address assignment in particular) that need the new device to not
yet be visible in the domaindef).

But hostdev interfaces short-circuit past most of the body of
qemuDomainAttachNetDevice() (since none of it applies to hostdev
interfaces). In the past that was okay, but since the line that adds
the new interface to the domaindef's nets list is in that "most of the
body", after that commit hotplugged hostdev interfaces are no longer
being properly added to the domaindef nets list, so they don't show up
in the status XML or the virsh domiflist output.

It really *is* important to add interfaces to the nets list earlier,
so we can't revert commit 7b8bec4560, and we also can't move the
insert to common code *earlier* in the function, so instead this patch
duplicates the VIR_APPEND_ELEMENT_COPY() just before the code path for
hostdev interfaces jumps to cleanup.

Resolves: https://bugzilla.redhat.com/1972468
Fixes: 7b8bec45601b6570f6a7413e94d291986d2663f1
Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>