Declare new utility functions for converting between the environment
variables (eth*addr) and the binary MAC address representation.  This way
we can unify all the random places that already do this kind of thing.

The functions in question:
	eth_parse_enetaddr - "..." -> {...}
	eth_getenv_enetaddr - env -> {...}
	eth_setenv_enetaddr - {...} -> env

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
CC: Ben Warren <biggerbadderben@gmail.com>