[TcpSlaveBase] port from KTcpSocket (deprecated) to QSslSocket

Summary: In setSslMetaData(), it's sufficient to add the cipher name

Reviewers: dfaure, vkrause

Reviewed By: vkrause

Subscribers: kde-frameworks-devel

Tags: Frameworks

Maniphest Tasks: T11544

Differential Revision: https://phabricator.kde.org/D24928