kernel - Reduce excessive inode hash table allocations

kernel - Reduce excessive inode hash table allocations

* Reduce excessive inode hash table allocations in various filesystems
  (primarily ufs).  Introduce vfs_inodehashsize() to calculate a reasonable
  hash table size instead of using 'maxvnodes'.

* The new formula is to generally use maxvnodes / 2 (2 x stacking for the
  chained hash table).  When maxvnodes is large we use maxvnodes / 4, and
  if maxvnodes is very large (> 1M vnodes) we use maxvnodes / 8.  This
  significantly reduces the amount of kernel memory used when mounting
  ufs, ext2fs, hpfs, isofs, msdosfs, nfs, ntfs, and smbfs filesystems.