Add support for 64-bit MAC addresses, fixes #5915

This would allow Infiniband interfaces to be managed by Foreman.  I have not tested this outside of local unit tests, so I would not consider it ready for merging.
I think we need to anchor each of these regexes with \A at the beginning, and \z at the end.  I tried entering a MAC of "aa:bb:cc:dd:ee:ff:gg:11" and hit an error on line 71, as the MAC matched the 48-bit regex but not the 64-bit, because the first 48 bits were correct.  It shouldn't have matched any of them really.