[9.20] fix: usr: Delay release of root privileges until after configuring controls
requested to merge backport-4793-bind-9-19-24-not-listening-to-rndc-port-953-on-localhost-9.20 into bind-9.20
Delay relinquishing root privileges until the control channel has been configured, for the benefit of systems that require root to use privileged port numbers. This mostly affects systems without fine-grained privilege systems (i.e., other than Linux).
Closes #4793 (closed)
Backport of MR !9123 (merged)