s3: Attempt to fix bug 7665

s3: Attempt to fix bug 7665

Quite a few of our internal routines put stuff on talloc_tos() these days.
In top-level netapi routines, properly allocate a stackframe and clean it
again. Also, don't leak memory in the rpccli_ callers onto the libnetapi
context.
(cherry picked from commit c4421a287c7e613c0c8da188a6ae8db37e90c8fc)