Instead of freeing host->ai on return from submit_request in the
http_proxy path, stash the proxy's ai in another member host->freeai
which will be freed when host is freed.
Assumption: All hosts created in submit_request cease to be used
before any of them are freed, so it's safe to pick one host to hang
the proxy's ai on and free the ai when that host is freed.
fix https://github.com/heimdal/heimdal/issues/1205
Taylor R Campbell
3171398867