Take a pretty version of an ethernet address and convert it to a
string of bytes.
The input string MUST be of the form xx:yy:zz:aa:bb:cc and leading
zero's must be supplied. Nor error checking is performed.
Take a set of bytes and convert them to a pretty version of
and Ethernet address.
The input buffer MUST be at least 6 bytes long and bytes after the
sixth are ignored. No error checking is performed.
