these would not be expensive to actually implement, but reading /etc/ethers does not sound like a particularly useful feature, so for now I'm leaving them as stubs.
based on patch by Strake with minor stylistic changes, and combined into a single file. this patch remained open for a long time due to some question as to whether ether_aton would be better implemented in terms of sscanf, and it's time something was committed, so here it is.