rpc: spkm3 update

This updates the spkm3 code to bring it up to date with our current
understanding of the spkm3 spec.

In doing so, we're changing the downcall format used by gssd in the spkm3 case,
which will cause an incompatilibity with old userland spkm3 support.  Since the
old code a) didn't implement the protocol correctly, and b) was never
distributed except in the form of some experimental patches from the citi web
site, we're assuming this is OK.

We do detect the old downcall format and print warning (and fail).  We also
include a version number in the new downcall format, to be used in the
future in case any further change is required.

In some more detail:

	- fix integrity support
	- removed dependency on NIDs. instead OIDs are used
	- known OID values for algorithms added.
	- fixed some context fields and types

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>