Add an option to enable communication between VMs

[devsunb]

Hello. I'm running two Linux VMs on macOS using tart and trying to configure them to communicate with each other, but I've been unsuccessful.
I tried to figure out why, and I've determined that the VM's network interface is being flagged PRIVATE when it is added as a member to the bridge network interface and this is because softnet sets enable_isolation to true when creating the vmnet network interface.
I think this makes sense since softnet was developed to isolate macOS VMs, but it would be nice to have an option to disable isolation for users with use cases like mine.