Don't assume MAC-addresses of 6 bytes #2828
Description
There are a few places in the code where we assume that the size of a MAC-address is exactly six bytes. That may not be correct in some places, as the newer EUI-64 kind can be eight bytes long. I'm not sure if we ever encounter the 20-octet InfiniBand ones, but either way we need to inspect the code and make sure that we handle that stuff gracefully.