Document nvme events
NVME generates events for all SMART critical events, as well as when we reset
the controller. Document these.
Add documenation for the HYPERV_NIC_VF subsystem
When the interface is configured, a message is generated to communicate if the
interface was brought up or taken down. Document that.
Document that CDEV/MEDIACHANGE events can be generated.
We also generate a MEDIACHANGE event on the cdev that changed.
Document the devctl events generated when an ethernet ifnet attaches.