Historically (and in a small amount of older software such as OpenAFS),
developers would attempt tofree XDR strings with
xdr_free((xdrproc_t)xdr_string, &string)

This resulted in xdr_free calling xdr_string with only two intentional
arguments and what ever was left in the third argument register. If the
register held a sufficently small number, xdr_string would return FALSE
and not free the string (noone checks the return values).

Software should instead free strings with:
xdr_free((xdrproc_t)xdr_wrapstring, &string)

Because buggy software exists in the wild, act as though xdr_wrapstring
was used in the XDR_FREE case and plug these leaks.

Effort: CHERI upstreaming
Sponsored by: Innovate UK