Give some kind of warning before rebooting VM when changing settings

[Red Squirrel]

I was testing something that involved nested virtualization, was in middle of an OS install on the hypervisor that was in a VM in Virtualbox. I realized I forgot to set Promiscious mode so I did that. I had no idea that would reboot the whole VM! No warning, no nothing.

It was just a test environment so not a huge deal, but rather annoying as it botched the install I was doing. If the setting can't be changed live then just allow to change it, and show a message indicating it will take effect next reboot, instead of force rebooting the VM.

[javispedro]

Normally most settings (including ethernet adapter settings except for "cable connected") are disabled (aka "greyed out") when the VM is running .