dns/powerdns: Adjust dependencies for tools

• Adjust dependencies (IXFRTOOL needs yaml-cpp)
• Explicitly disable decaf and sodium in case they are not enabled. Otherwise they default to "auto" and if detected in the system, stage-qa reports unresolved dependency.
• Drop user privilges for worker processes to pdns/pdns (UID is new; GUID already exists)
• Always depend on protobuf. I do the same for dnsdist and powerdns-recursor
• Actually do something with the pdns_flags variable in the rc-script instead of just mentioning it in the comment block
• Bump PORTREVISION

PR: 250961
Submitted by: Juraj Lutter, Ralf van der Enden
Approved by: Ralf van der Enden (maintainer)