opr: Add opr_jhash_int2 function

Add a function to jhash that can be used to hash a pair of unsigned
integers (or other stuff that can cast to them) without having to build
up an array.

Provide a couple of tests for the new function

Reviewed-on: http://gerrit.openafs.org/8354
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 07372cf7e76acf62eb26908977e2682338c85ac1)

Change-Id: I944d8308dbda1cf1989b1d8497486f8463d1aacb
Reviewed-on: http://gerrit.openafs.org/10630
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: BUF_HASH use opr_jhash_int2

BUF_HASH takes to 4-byte integers not three and therefore cannot use
the basic opr_jhash which assumes a minimum of three 4-byte integers.

Reviewed-on: http://gerrit.openafs.org/10624
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 4f1d4b63a90e85fd0c2edc592d18bdbe6a0b07f8)

Change-Id: Ia1c879cb809fbad493398dc42127f32cf7a8ad13
Reviewed-on: http://gerrit.openafs.org/10626
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>