SUNRPC: Make spkm3 report unsupported encryption types

 Print messages when an unsupported encrytion algorthm is requested or
 there is an error locating a supported algorthm.

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