Maintain Vrefmain setting when running the ASIC config ("hxconfig")

The configuration call to the ASIC sets up the geometry, etc. for the ASIC and the detector. It does not change the bias voltages for the detector (e.g. VReset or DSub). But it turns out that the ASIC's preamp bias level is changed. Whether that is from the actor or library doing something wrong, or from the ASIC call itself doing something unexpected, that needs to be changed: a call to the ASIC config routine with a configuration identical to the running one should have no effect.