fix: usr: Delay release of root privileges until after configuring controls

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

Merge branch '4793-bind-9-19-24-not-listening-to-rndc-port-953-on-localhost' into 'main'

Closes #4793

See merge request isc-projects/bind9!9123