Create isc_managers API
All the BIND 9 binaries have the same sequence of taskmgr/netmgr/timermgr/... ctors and dtors. Move this into a separate API, so we don't duplicate the code at various places.
All the BIND 9 binaries have the same sequence of taskmgr/netmgr/timermgr/... ctors and dtors. Move this into a separate API, so we don't duplicate the code at various places.