sion (rpcb now returns EPFNOSUPPORT)

This change allows more specific error processing for each of these two
cases.  We now fail case 2 instead of retrying... it's a server
configuration error not to support even rpcbind version 2.  And don't
expose this new error code to user land -- convert it to EIO before
failing the RPC.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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