The old MAC allocator had several drawbacks:
* the address base was a public static that could and must have been written
directly from outside the class
* the in-use-flag array was based on unsigned values consuming 4 bytes each
for only one bit of information
* it was a public header that we actually don't want to expose to all
components but only to the few networking components
* it used the not-so-safe bit notation for integer members of GCC
The new version fixes all these drawbacks.
Issue #2795