The BOOTIF MAC address can be prefixed with a hardware address type. Typically it is 01 (for ethernet), but the legacy network module accepts (and strips) any byte value.
It seems wrong to take any address type without validation. In addition to "01", also accept a zero type which, according to the bugzilla below, is used in some configurations to mean "undefined".
While at it, also accept ':' as separator for the first byte.