Extract the mac address from provided address. None is returned
    on error.

def in6_addrtomac(addr):
    """
    Extract the mac address from provided address. None is returned
    on error.
    """
    mask = inet_pton(socket.AF_INET6, "::ffff:ffff:ffff:ffff")
    x = in6_and(mask, inet_pton(socket.AF_INET6, addr))
    ifaceid = inet_ntop(socket.AF_INET6, x)[2:]
    return in6_ifaceidtomac(ifaceid)