proto_cc_dupfid
rv = proto_cc_dupfid(pu, fid, newfid);
int proto_cc_dupfid(struct puffs_usermount *, p9pfid_t, p9pfid_t);
rv = proto_cc_dupfid(pu, p9n->fid_base, nfid);
rv = proto_cc_dupfid(pu, p9n->fid_base, testfid);