Fix a couple of things in the internal mbuf allocation interface:
Fix a couple of things in the internal mbuf allocation interface:

- Make sure that m_mballoc() really doesn't allow over nmbufs mbufs to
  be allocated from mb_map. In the case where nmbufs-reserved space is not
  an exact multiple of PAGE_SIZE (which it should be, but anyway...), we
  hold nmbufs as an absolute maximum which need not ever be reached.

- Clean up m_clalloc(); make it more consistent in the sense that the first
  argument `ncl' really means "the number of clusters ensured to be allocated"
  and not "the number of pages worth of clusters to be allocated," as was
  previously the case. This also makes it consistent with m_mballoc() as well
  as the comment that preceeds it.

Reviewed by: jlemon

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