qga: Utilize QAPI_LIST_APPEND in qmp_guest_network_get_interfaces

I found another spot that can benefit from using our macros instead of
open-coding qapi list creation.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210205171634.1491258-1-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
1 file changed