Forcing maxsize to RPC_MAXDATASIZE breaks code that deliberately uses
XDR with longer strings than permitted by SunRPC.
MFC after: 1 week
Fixes: 6448ec89e739 (" * limit size of buffers to RPC_MAXDATASIZE")
Fixes: e17d7ab869bb ("xdr_string: don't leak strings with xdr_free")
Sponsored by: Klara, Inc.
Sponsored by: NetApp, Inc.