smb: do not leak pbsd resolvers

Summary:
parent them to the discoverer. discoverer lives on the stack and is unwound
once discovery is complete (or the eventloop timeout hit)

Test Plan: made a dtor that qdebugged, dtor is now executed as expected

Reviewers: ngraham

Reviewed By: ngraham

Subscribers: kde-frameworks-devel, kfm-devel

Tags: Dolphin, Frameworks

Differential Revision: https://phabricator.kde.org/D27901