vnicserver device needs to signal to phyp when it's shutting down to avoid network outage

Environment:
Power9 server with vios 3.1.3.21 pair which host vnicserver devices with backing sriov adapters for the vnic client devices in failover configuration

Problem:
During shutdown/reboot of the vio server that hosts the active vnicserver device for a client lpar the client lpar experiences a network outage of about 10 seconds.
When doing a manual vnic failover from the HMC, the network outage is less than 3 seconds.

Analysis of the phyp support team:
Since it sounds like this is especially prevalent during VIOS shutdown, I'm wondering how events are sequenced in the VIOS during a shutdown. During normal operation, the VIOS reports failover status down to the hypervisor at regular intervals to indicate that the device is still operational. If the hypervisor does not receive status within a timeout period, the adapter is deemed unresponsive and a failover occurs. I would hope that the VIOS reports a non-operational status if they know they are shutting down, as that would cause the hypervisor to failover immediately. If the VIOS instead simply stops sending us events, it can take some time for the hypervisor to determine that the VIOS is unresponsive. From recent traces it looks like that timeout period is about 3 seconds - that's about how long it would take for us to initiate the failover if the VIOS suddenly becomes unresponsive. 

Analysis of the vnicserver device driver team:
vNIC failover is initiated by Hypervisor and looks like HMC has a mechanism to communicate to Hypervisor to trigger vNIC failover. But VIOS doesn’t have a such mechanism to communicate to Hypervisor to trigger vNIC failover, rather Hypervisor do failover when it detects VIOS is down, this process takes a little extra time and hence more n/w breakage to vNIC client while VIOS is getting down.
So, to reduce network breakage during VIOS reboot, vNICServer team and Hypervisor team should collaborate and come up with a mechanism, perhaps the way HMC and Hypervisor established it as of now. This is a development effort and hence need an RFE.