Use the zone allocator to allocate inpcbs and tcpcbs. Each protocol creates

Use the zone allocator to allocate inpcbs and tcpcbs.  Each protocol creates
its own zone; this is used particularly by TCP which allocates both inpcb and
tcpcb in a single allocation.  (Some hackery ensures that the tcpcb is
reasonably aligned.)  Also keep track of the number of pcbs of each type
allocated, and keep a generation count (instance version number) for future
use.