Set the IPv6 adapter IP to be <prefix>::1. Otherwise, guest to host communication over IPv6 is not routed correctly. This means that consumers should not specify <prefix>::1 IP addresses to VirtualBox, which should be a reasonable restriction. Fixes #6658
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.