[PATCH] libvirt: ensure defresult is used in virConnectAuthCallbackDefault

[Matt Coleman]

Some additional info (feel free to add it to the commit message):

Starting in version 6.1.0, virsh does not use the default username while connecting:

$ ./run tools/virsh -c hyperv://example-hyperv-server?transport=http capabilities
Enter username for example-hyperv-server [administrator]:
Enter 's password for example-hyperv-server:
error: failed to connect to the hypervisor
error: internal error: Transport error during enumeration: User, password or similar was not accepted (26)
$ ./run tools/virsh -c hyperv://example-hyperv-server?transport=http capabilities
Enter username for example-hyperv-server [administrator]: administrator
Enter administrator's password for example-hyperv-server:
<capabilities>
  <host>
…

I’ve reproduced this on several versions of Fedora and Ubuntu 20.04. You can reproduce it locally (although with a slightly different error) by replacing example-hyperv-server with 127.0.0.1.

-- 
Matt