rename of M_ alloc defines

[Jeffrey Hsu]

Hiten Pandya wrote:

    You still need to rename the libmchain flags as I have mentioned
    quite a few times before.  They are named MB_*, and they should
    be renamed to MBC_* to avoid confusion.
I see a lot of confustion between the mbuf allocation M_ flags and
the malloc M_ flags.  I do not see a lot of confusion between the
mbuf flags and the libmchain flags.  So let's keep the two issues
and patches separate please.
									Jeffrey