In oVirt 4.1 switch type allowed to set linux bridge or ovs experimetal.
In oVirt 4.2 switch type is set to linux bridge and is disabled in the web ui, not allowing different choice.
If no choice is possible, it would be better to drop the config.
If the field is disabled missing a requirement, a tool tip should say what's missing.
This bugzilla is included in oVirt 4.2.5 release, published on July 30th 2018.
Since the problem described in this bug report should be
resolved in oVirt 4.2.5 release, it has been closed with a resolution of CURRENT RELEASE.
If the solution does not work for you, please open a new bug report.