SUNRPC: rsi_parse() should use the current user namespace

rsi_parse() is part of a downcall, so we must assume that the uids
and gids are encoded using the current user namespace.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>