kasp: when switching from KSK/ZSK to CSK, upgrade KSK to CSK
When BIND switches from KSK/ZSK to CSK, instead of creating a new key, it could promote the KSK to CSK and withdraw the ZSK.
When BIND switches from KSK/ZSK to CSK, instead of creating a new key, it could promote the KSK to CSK and withdraw the ZSK.