SUNRPC: Use rpc_ntop() for constructing transport address strings

Clean up:  In addition to using the new generic rpc_ntop() and
rpc_get_port() functions, have the RPC client compute the presentation
address buffer sizes dynamically using kstrdup().

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