Need a way to acknowledge when Hubris disables a module

[Aaron-Hartwig]

When something goes awry during the SPs thermal monitoring of a module it will take the following action:

• Power down the module
• Hold it in reset
• Deassert LPMode (to account for the 3.3V leakage when this is driven to some unpowered modules)
• Mark in Hubris that this port has been disabled by policy

That last bullet point has the following effects:

• All messages from the host to change this module will be rejected (need a new HwError variant for this)
• Need a new HostRequest message to clear the policy

cc: @mkeeter