opr: Make opr_uuid_hash endian-independent

opr: Make opr_uuid_hash endian-independent

And also make sure it doesn’t use unaligned accesses.  Fixes a ‘make
check’ failure on big-endian architectures.

Change-Id: I490174f8d1eecb5f20969b4ef12ff16d0dd3806a
Reviewed-on: https://gerrit.openafs.org/12495
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: Michael Meffie <mmeffie@sinenomine.net>