D27603: KDNSSD: Convert license headers to SPDX statements

[Andreas Cord-Landwehr]

cordlandwehr added a task: T11550: Add SPDX License markers.

REPOSITORY
  R272 KDNSSD

REVISION DETAIL
  https://phabricator.kde.org/D27603

To: cordlandwehr
Cc: kde-frameworks-devel, LeGast00n, cblack, GB_2, michaelh, ngraham, bruns