Dual stack VIPs incompatible with EnableUnicast setting

This is a clone of issue OCPBUGS-12729. The following is the description of the original issue:
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Description of problem:

This came out of the investigation of https://issues.redhat.com/browse/OCPBUGS-11691 . The nested node configs used to support dual stack VIPs do not correctly respect the EnableUnicast setting. This is causing issues on EUS upgrades where the unicast migration cannot happen until all nodes are on 4.12. This is blocking both the workaround and the eventual proper fix.

Version-Release number of selected component (if applicable):

4.12

How reproducible:

Always

Steps to Reproduce:

1. Deploy 4.11 with unicast explicitly disabled (via MCO patch)
2. Write /etc/keepalived/monitor-user.conf to suppress unicast migration
3. Upgrade to 4.12

Actual results:

Nodes come up in unicast mode

Expected results:

Nodes remain in multicast mode until monitor-user.conf is removed

Additional info: