fdo#75328 Do DiscoveryService socket setup off the main thread.

Change-Id: I795f365981d8e7983c9f32531c9ec2ae4793c8f4
(cherry picked from commit c0fb2640665d552b39deb2192d59fa11ea701d51)
Reviewed-on: https://gerrit.libreoffice.org/8643
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>