Add network and synced_folder default configuration for vagrant

[heliocentric_gmail.com]

Summary

This adds two missing parts of the base box, the network adapter base mac address, and the default sync provider to rsync.

Both of these are required for OOB use of the freebsd boxes without additional configuration, particularly in automated acceptance testing frameworks.

[heliocentric_gmail.com]

Allocate from the freebsd oui list, and document it in the correct place