For consistency sake, use >= MINCLSIZE rather than > MINCLSIZE to determine

For consistency sake, use >= MINCLSIZE rather than > MINCLSIZE to determine
whether or not to allocate a full mbuf cluster rather than just a plain
mbuf when adding on additional mbufs in m_getm().  In practice, there wasn't
any resulting mem trashing since m_getm() doesn't ever allocate an mbuf with
a packet header, and MINCLSIZE is the available payload in an mbuf with a
header rather than the available payload in a plain mbuf.

Discussed with: 	andre (lightly)