afs: use jenkins hash for dcache, vcache tables

afs: use jenkins hash for dcache, vcache tables

Switch the four dcache and vcache hash tables to use the jenkins
hash from opr.

This requires making DCHash into a full-weight function in order
to properly hash all three inputs; convert all four symbols to
full functions for consistency.  Just pull in <opr/jhash.h> via
afs.h so all consumers (e.g., of VCSIZE) can use it without
modification.

This is the first use of src/opr/ in src/afs/ (outside UKERNEL),
but it is permissible because opr/jhash.h is a standalone
header and there are no C files needed for its implementation which
would require anything from the system.

Change-Id: Ic7f31e7dc548ff2cf13ac087a9e4bbb2b874e03a
Reviewed-on: http://gerrit.openafs.org/11673
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>