Creates an ONC RPC client handle for the remote program prognum,
    version versnum at address addr. The client uses UDP as the
    transport. The routine is similar to the clnt_create routine,
    except clntudp_create allows you to specify a socket and the UDP
    retransmission time.

    If you specify the port number as zero by using addr->sin_port,
    the Portmapper provides the number of the port on which the
    remote program is listening.

    The clntudp_create routine uses the global variable rpc_
    createerr. rpc_createerr is a structure that contains the most
    recent service creation error. Use rpc_createerr if you want the
    client program to handle the error. The value of rpc_createerr is
    set by any RPC client creation routine that does not succeed. The
    rpc_createerr variable is defined in the CLNT.H file.

    The socket referenced by sockp is copied into a private area for
    RPC to use. It is the client's responsibility to close the socket
    referenced by sockp.

    The authentication scheme for the client, client->cl_auth, gets
    set to null authentication. The calling program can set this to
    something different if necessary.

                                  NOTES
       Since UDP/IP messages can only hold up to 8 KB of encoded
       data, this transport cannot be used for procedures that take
       large arguments or return huge results.

       If addr->sin_port is 0 and the requested program is
       available on the host but the program does not support the
       requested version number, this routine still succeeds. A
       subsequent call to the clnt_call routine will discover the
       version mismatch. Use the clnt_create_vers routine if you
       want to avoid this condition.