add some helpers for working with ethernet addresses as uint64_t

add some helpers for working with ethernet addresses as uint64_t

the main bits are ether_addr_to_e64 and ether_e64_to addr for loading
an ethernet address into a uin64_t and visa versa. there's also
some macros for testing if an address in a uint64_t is multicast,
broadcast, anyaddr, or if it's an 802.1q reserved multicast group
address.

the reason for this functionality is once you have an ethernet
address as a uint64_t, operations like compares, bit tests, and
so on are fast and easy.

tested on amd64 and sparc64