KDNSSD: Convert license headers to SPDX statements
Summary:
Convert license headers to SPDX statements and add license files
as required by SPDX specification
Reviewers: cgiboudeaux
Reviewed By: cgiboudeaux
Subscribers: kde-frameworks-devel
Tags: Frameworks
Maniphest Tasks: T11550
Differential Revision: https://phabricator.kde.org/D27603