SUNRPC: Add RFC 8009 checksum KUnit tests

RFC 8009 provides sample checksum results. Add KUnit tests to ensure
our implementation derives the expected results for the provided
sample input.

Tested-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>