This commit will generate a static MAC address for each jail, based on the name of the jail. It will use the first half (xx:xx:xx) of the host MAC to avoid network clashes, and generate a random HEX string from the hashed name of the jail. It will then add that random 5 character HEX string in MAC format, and add an "a" and "b" for the host and jail respectively.
This way a jail can retain it's MAC ID even if it is deleted and reinstalled, as long as the same name is retained.
There's quite a bit more we could do here, but this hits my basic usage
with vnets. Future work here would be things like ipv6 support or trying
to infer what a custom `interfaces` setting means.
