MFC: r225537

MFC: r225537
Modify vfs_register() to use a hash calculation
on vfc_name to set vfc_typenum, so that vfc_typenum doesn't
change when file systems are loaded in different orders. This
keeps NFS file handles from changing, for file systems that
use vfc_typenum in their fsid. This change is controlled via
a loader.conf variable called vfs.typenumhash, since vfc_typenum
will change once when this is enabled. It defaults to 1 for
9.0, but will default to 0 when MFC'd to stable/8.

git-svn-id: svn://svn.freebsd.org/base/stable/8@226926 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f